ase of the Mott translation. There is no mention of frames of reference, inertial or otherwise.
A respected and influential modern textbook, aimed at a much higher level than Millikan's book, is Kleppner and Kolenkow's 1973 Introduction to Mechanics. K&K has this:

...it is always possible to find a coordinate system with respect to
  which isolated bodies move uniformly. [...] Newton's first law of
  motion is the assertion that inertial systems exist. Newton's first
  law is part definition and part experimental fact. Isolated bodies
  move uniformly in inertial systems by virtue of the definition of an
  inertial system. In contrast, that inertial systems exist is a
  statement about the physical world. Newton's first law raises a number
  of questions, such as what we mean by an 'isolated body,' [...]

There is a paper on this historical/educational topic: Galili and Tseitlin, "Newton's First Law: Text, Translations, Interpretations and Physics Education," Science & Education
Volume 12, Number 1, 45-73, DOI: 10.1023/A:1022632600805. I had access to it at one time, and it seemed very relevant. Unfortunately it's paywalled now. The abstract, which is not paywalled, says, 

Normally, NFL is interpreted as a special case: a trivial deduction
  from Newton's Second Law. Some advanced textbooks replace NFL by a
  modernized claim, which abandons its original meaning.

Question 1: Does anyone know more about when textbooks begain to claim that the first law was a statement of the definition and/or existence of inertial frames?
There seem to be several possible interpretations of the first law:
A. Newton consciously wrote the laws of motion in the style of an axiomatic system, possibly emulating Euclid. However, this is only a matter of style. The first law is clearly a trivial deduction from the second law. Newton presented it as a separate law merely to emphasize that he was working in the framework of Galileo, not medieval scholasticism.
B. Newton's presentation of the first and second laws is logically defective, but Newton wasn't able to do any better because he lacked the notion of inertial and noninertial frames of reference. Modern textbook authors can tell Newton, "there, fixed that for you."
C. It
ase of the Mott translation. There is no mention of frames of reference point, inertial or differently. 
 A respected and influential modern textbook, aimed at a a lot higher horizontal surface than Millikan's book, is Kleppner and Kolenkow's 1973 Introduction to Mechanics. K&K have this: 

... it is always possible to find a coordinate system with respect to 
   which apart bodies move uniformly. [... ] Newton's inaugural law of 
   motion is the assertion that inertial systems exist. Newton's first 
   jurisprudence is part definition and part experimental fact. Isolated body 
   move uniformly in inertial systems by virtue of the definition of an 
   inertial system. In line, that inertial systems exist is a 
   affirmation about the physical world. Newton's first police raises a number 
   of questions, such as what we mean by an' isolated soundbox,' [... ] 

 There is a paper on this historical / educational topic: Galili and Tseitlin, " Newton's First Law: Text, Translations, Interpretations and Physics Education, " Science & Education 
 Volume 12, Number 1, 45 - 73, DOI: 10.1023 / A:1022632600805. I had access to it at one time, and it seemed very relevant. Unfortunately it's paywalled now. The abstraction, which is not paywalled, says, 

 Normally, NFL is interpreted as a limited casing: a trivial deduction 
   from Newton's Second Law. Some advance textbooks supplant NFL by a 
   modernized claim, which abandon its original meaning. 

 Question 1: Does anyone know more about when textbooks begain to claim that the first police was a statement of the definition and/or existence of inertial frames? 
 There seem to be respective possible interpretation of the inaugural law: 
 A. Newton consciously wrote the laws of motion in the stylus of an axiomatic system, possibly emulating Euclid. However, this is only a matter of style. The first law is clearly a superficial deduction from the second police. Newton presented it as a separate jurisprudence merely to emphasize that he was ferment in the framework of Galileo, not chivalric scholasticism. 
 B. Newton's presentation of the first and second law is logically defective, but Newton wasn't able to do any good because he lacked the impression of inertial and noninertial frames of reference. Modern textbook generator can tell Newton, " there, fixed that for you. " 
 C. It
ase of the Mott translation. There is no meurion oh framea of refdrence, inertial or otherwise.
E rewpecttb and influential moaern texthook, aimwd au a much higher lxbel thak Milmlkan's uook, is Kleppnet and Kolenkmw's 1973 Introducthov co Mechanics. K&K has this:

...it is always possibke to find a cootdinaue fystsm with respect to
  which isolated bodies move uniformky. [...] Newton's first law of
  lotiln is the assertioj that inerjjal wystems exisg. Newton's first
  law ia part definition and part expefimencal fact. Isilqtef bodies
  mote unisormly in incgtial sfstems ny virtue of tme dehinirion of an
  inertial vystem. In contrast, that inestnal systems exist is q
  statgment abojr tfe khyxidal wogld. Newton's fjrst law rauses a number
  of qiefnoons, such as what re mean by an 'isolated body,' [...]

There is a paker oh this historical/educatuonal topic: Galili anf Tseitlig, "Newton's First Law: Text, Translations, Interpretathons ena Pknfkxs Education," Science & Education
Volume 12, Number 1, 45-73, SOO: 10.1023/S:1022632600805. I had access to it at ome toie, and it seeoed vexg delevant. Unfortunahely it'f payqalled nor. Thr abstract, which is not payqalled, says, 

Uornally, NFL is inter'reted as a rpecoal csse: a trivial deduction
  frkm Newton's Decond Las. Some advanced tdxtnoons replace NFL by a
  modergized clamm, whnch abanaons its owiginal mewning.

Question 1: Does anyoje knlw more abouh when textbooks begain to claim that the firxt laf was a ftatekent of the dqfinition and/ot existenee of knertial fgames?
Therx seem to be several posshhle interprevations os thw fiest law:
X. Newton conscipusly wrone the laws of motion in thg atyle of an axiimauix system, possinly emtlwtmng Etwlid. However, thir ir only a matttx on sgyle. The first law is claarlg a trivial deductook from thg second jaw. Newton prrsented it as a sekarate lax mereky jo emphasize that he was workinf in the vraiework of Gajilei, not medievcl scholasticism.
B. Newton's presentation oh the first and second oaws is logically dgfegtive, but Nexton wwsn't able to do any better bexause he lacked tme notion of inertial znd notinerhial frames of reference. Modern textbook authors can tell Newton, "there, fized thet for you."
C. If
ase of the Mott translation. There is of of reference, or otherwise. A aimed a much higher than Millikan's book, Kleppner and Kolenkow's 1973 Introduction to K&K has this: ...it is always possible to find a coordinate system with to which isolated bodies move uniformly. [...] Newton's first law of motion is assertion inertial exist. first law is part definition and part experimental fact. Isolated bodies move uniformly in inertial systems virtue of the definition of an inertial system. contrast, that inertial systems is a statement about the world. first law a of such as what mean by an 'isolated body,' [...] There is a paper on this historical/educational topic: Galili and Tseitlin, First Law: Interpretations and Education," & Volume 12, Number DOI: 10.1023/A:1022632600805. I had access to time, and it seemed very relevant. Unfortunately it's now. The which is not paywalled, says, Normally, is interpreted as a special case: a trivial from Newton's Second Law. Some advanced textbooks replace NFL by a modernized claim, which abandons meaning. Question 1: Does know more about textbooks to that first law a statement of the definition and/or existence of inertial frames? There to be several possible interpretations of the first law: A. wrote laws of motion the style of an system, emulating Euclid. However, this a of law clearly trivial deduction from the law. Newton presented it as separate law merely to in the framework of Galileo, not medieval scholasticism. Newton's presentation of the first and second is logically defective, but Newton wasn't able to do any better because lacked the inertial and noninertial frames of reference. Modern textbook can tell Newton, "there, that for you." C. It
ase of the Mott translation. ThEre is no menTion oF frAmeS oF refErenCe, inertial or otHErwiSe.
A respected and influenTial mOdERn teXTbOok, aiMed at a mUCh HIGheR lEvEl tHaN miLlikaN's bOok, is KlEppner and KOleNkOw's 1973 IntroductIOn To MechanicS. K&K Has this:

...it is aLwaYs possIbLe tO Find a CooRdinaTe systEM with rEspect to
  wHiCH isolaTEd bodieS MOvE uniFormly. [...] Newton's firsT LaW Of
  motion is the aSsertiOn THaT INerTiaL systems exIsT. NewtON's first
  LAw IS PArt DEfinition and pArt experimeNTal Fact. IsOlAteD Bodies
  Move uNiFOrmLy in inertiaL sysTems by virTue of tHE definiTIon of an
  InertiAl sYstEm. In COnTrAst, ThAT inERtIal SYstEms exist Is A
  sTatemEnt aBOUT The pHysIcal World. newton's first lAw rAiseS A nuMber
  oF quesTionS, sUch as What we Mean bY aN 'isolated body,' [...]

ThEre iS a paper on ThiS hIstOrIcal/eDUcatioNal TopIc: GalilI and TseITliN, "NEWTOn'S First Law: Text, TransLaTIOnS, InterprEtatioNS aNd pHysics EdUcAtiOn," ScIENce & EdUcatIOn
volume 12, NuMber 1, 45-73, DOi: 10.1023/a:1022632600805. I HaD access To It at onE tIme, And It seeMEd veRy releVant. UnfoRtunaTEly it's paywalleD Now. The abstracT, WhICH iS Not pAywAlled, says, 

NoRmalLY, NFL Is inTErPreTEd as a SpeciAl CAsE: A trivial deduction
  frOm newton'S SecoNd Law. Some advaNced textboOKS Replace NfL by A
  MoDErnized claim, whIch abAndons its oRIginal meAning.

question 1: does anyonE KNow more aBouT whEn tExtBOOkS begain to claiM THat tHe First laW waS a stateMenT of The DefInItion and/oR existenCe Of InErTiaL framES?
There seEm To bE sEveRal poSSible iNterpRetaTiOnS Of tHe first LAw:
a. nEwtoN cOnScioUslY wRote tHe laWS of Motion iN the style Of aN AxioMaTiC system, Possibly emulaTiNg Euclid. HoWeVer, This is ONLy a matteR of style. The first law is clEArly a trIviAl dedUctiOn from the SecOnd law. newTOn presEnted iT as a sEpAraTE Law meRELy To eMpHasize that HE Was WorkiNg In thE framewOrk of Galileo, not medIEvaL scholasticisM.
B. NEwtoN'S PrEseNTaTIon Of THe fIRSt and second laws Is logicallY dEFeCtive, but NeWTon WaSn't able To do any BetteR Because He lacked tHe notion oF iNertIAL anD noninertiAl frames Of referenCE. ModeRN tExtboOk aUthors CaN teLl NewTon, "theRE, fiXed thAt for yOu."
c. It
ase of the Mott translatio n. There i s nomen tio nof f rame s of reference ,  ine rtial or otherwise.
Arespe ct e d an d  i nflue ntial m o de r n  te xt bo ok,  a i me d ata m uch hig her leveltha nMillikan's b o ok , is Klepp ner  and Kolenko w's  1973In tro d uctio n t o Mec hanics .  K&K h as this:
. . .it is alwaysp o ss ible  to find a coordi n at e  system with r espect  t o 
w hic h i solated bo di es mo v e unifo r ml y . [.. . ] Newton's fi rst law of mo tion i sthe assert ion t ha t  in ertial syst emsexist. Ne wton's first
law ispart d efi nit iona nd  p art  e x per i me nta l  fa ct. Isol at ed  bodi es
m o v e un ifo rmly  in i nertial syste msby v i rtu e ofthe d efin it ion o f an
 iner ti al system. In c ontr ast, that  in er tia lsyste m s exis t i s a 
  stat ement a b out  t h e ph ysical world. Newt on ' s  f irst law  raise s  a  n u mber
  o fque stio n s , suc h as wh at we me an bya n'i solated  b ody,'[. ..] 

T herei s apaperon thishisto r ical/education a l topic: Gali l ia n dT seit lin , "Newton's  Fir s t La w: T e xt , T r ansla tions ,I nt e rpretations and Phy si cs Edu catio n," Science &  Education V o lume 12,  Num b er 1, 45-73, DOI:  10.1 023/A:1022 6 32600805 . I h ad acces s to it a t one time , a nditsee m e dvery relevant . Unfo rt unately  it 's payw all ednow . T he  abstract , whichis  n ot  p ayw alled ,  says, 
N orm al ly,  NFLi s inte rpret ed a sas pec ial cas e :a triv ia ldedu cti on 
  fr om N e wto n's Sec ond Law.Som e  adv an ce d textb ooks replaceNF L by a
  m od ern ized c l a im, whic h abandons its original meaning .
Quest ion1: Does a nyo ne kno w m o re abo ut whe n tex tb ook s begai n to  cl ai m that the f irs t law  w as a  statem ent of the definit i onand/or existe nce  ofi n er tia l  f r ame s? The r e  seem to be sev eral possi bl e  i nterpretat i ons  o f the f irst la w:
A. Newtonconscious ly wroteth e la w s  of  motion in  the sty le of ana xioma t ic  syst em,  possi bl y e mulat ing Eu c lid . How ever,th is isonlyamatter o f style. The first lawis cle arlya t rivial de duc t ion  from the  sec ond law. N ewt onprese nte d  it a s as ep ara t e law  mer e ly to emp h as ize t ha t he was wo r k i ngin th e f r amewor k of  Galileo, not med i eval scholasti cism . B.New t on's  p resentation of  th ef i rst andse cond laws i s logica ll y  defe ctive,  but N ewton w a s n' t  ableto d o a ny better  be ca u se he l ac ke d  the n otio nof ine rtiala nd n o n inertial framesof re f e rence .  Mo dernte xtbooka utho rs can tel l Newton, " there,  fix ed th at foryo u."
C.  It 
ase of_the Mott_translation. There is no_mention of_frames_of reference,_inertial_or otherwise.
A respected_and influential modern_textbook, aimed at a_much higher level_than_Millikan's book, is Kleppner and Kolenkow's 1973 Introduction to Mechanics. K&K has this:

...it is_always_possible to_find_a_coordinate system with respect to
_ which isolated bodies move_uniformly. [...]_Newton's first law of
  motion is the_assertion_that inertial systems_exist. Newton's first
  law is part definition and_part experimental fact. Isolated bodies
 _move uniformly in_inertial_systems_by virtue of the_definition of an
  inertial system._In contrast, that inertial systems exist_is a
  statement about the physical_world. Newton's first law raises a_number
  of questions, such_as what_we mean by an 'isolated_body,' [...]

There is_a paper_on this historical/educational_topic: Galili and Tseitlin, "Newton's First_Law: Text, Translations,_Interpretations and Physics Education," Science &_Education
Volume_12, Number 1,_45-73,_DOI:_10.1023/A:1022632600805. I_had access to_it_at one_time,_and it seemed very relevant. Unfortunately_it's_paywalled now. The abstract, which is not_paywalled, says, 

Normally, NFL_is_interpreted as a special_case: a trivial deduction
 _from Newton's Second Law. Some advanced_textbooks replace_NFL by_a
  modernized claim, which abandons its original meaning.

Question 1: Does_anyone know more about when textbooks_begain to claim that_the first_law_was a statement_of_the definition_and/or existence of inertial frames?
There seem to_be several_possible interpretations of the first law:
A._Newton consciously wrote the_laws_of motion in the style of_an axiomatic system, possibly emulating Euclid._However, this is only a_matter_of_style. The first law is_clearly a trivial deduction from the_second law. Newton_presented it as a separate law merely_to_emphasize that he was working in_the_framework of Galileo, not medieval scholasticism.
B._Newton's_presentation_of the first and second_laws is logically defective, but Newton_wasn't able to do any better because he lacked_the notion of_inertial and noninertial frames of_reference._Modern_textbook authors can tell Newton, "there, fixed that for you."
C._It