help me interpret the results of an outlet tester on some GFCI receptacles
Normally, the legends on a 3-light tester are useless and wrong, so I call them "magic 8-ball testers".   However, they are simple affairs, with the 3 neon lights connected triangle style across the 3 prongs, and a thinker can get useful info out of that.

Not in your case.  That tester has a microcontroller stuck in front of the lights. The controller is interpreting the raw signals to "help you out". Just like the old legends, the interpreted answers are wrong.   So it destroyed the one thing that made a 3-lamp tester useful: raw data. Into the trash it goes.

Get an old style one, with yellow yellow red lights and Y Y - being a normal reading. 

Of course get one with a GFCI tester; that function has nothing to do with the presence or absence of the very unhelpful microcomputer.



I agree with your analysis on receptacles 2, 3 and 4.  GFCI #1, ??? Whatever.  It is normal for outdoor GFCIs to fail far too soon, that's what you get for leaving them outside.  Occam's razor: bad GFCI.  



Do you know how GFCIs work?   "I spend $20 a socket replacing every receptacle with one of these and the home inspector signs off" is not how GFCIs work.  

GFCI is a filtering/safety system that rides between the hot and neutral.  It comes in combo w/breaker, standalone (deadfront) or combo w/receptacle.  Obviously, the first two don't have any sockets and their one thing is to protect the downline part of the circuit.  They can protect the whole circuit - one device. 

Here's the thing: the common GFCI receptacle can do that too. That's the one purpose of the LOAD terminals.  

So when I hear about GFCIs getting chewed up outdoors, and when I hear about 2 GFCIs on the same circuit, I say it's a good time to figure how the circuit is wired, and find an indoor location to fit one GFCI that'll protect the whole outdoor part of the circuit.