Is everything in order?
05AB1E, 10 ... 172 distinct bytes

\]^_abcdefghiijklmnopqrstuvwxyz{|}}}~ƵƵ€Λ‚„…†‡ˆ‰ŠĆĆĆŽƶĀ‘‘’’““””••–—™š›œćŸā¡¢¢¢¤¤¦§¨©ª«¬®¯°±´¶·¸º»¼½½¾¿ÀÁÁÂÃÄÅÇÌÍÐÐÐÐÐÐÑÒÓÔÕÖ×ØÙÚÛÜÝßàáâãäåçèéêëìíîïðñòóôõö÷úü
 -.0123456789;&lt;&gt;@ABCDDDHKKOPQRSTUVWXYZ


Try it online! or validate all test cases (note: the "all test cases" version omits ] and ë, since those don't play well with the header and footer required to run the code repeatedly).

Uses the 05AB1E code page. Validate restricted-source and scoring.

The useful code is just:

Ć            # append the first character of the input to the input
 Ç           # convert to a list of codepoints
  ü-         # pairwise subtraction
    1@       # &gt;= 1?
      D      # duplicate
       O     # sum
        Q    # equal?
         Z   # maximum


The rest amounts to NOOPs.