Right up there on the Anooyance Scale with Peter David re-naming Arex's race the "Triexians" (cuz they got three legs and three arms! get it? huh? get it?).
Of course, he was totally within his right to come up with a name for Arex's species.
M'Ress had her home planet, Cait, and its location (Lynx Constellation) specifically named in the TAS Writers' Bible (which was essentially the TOS Writers' Bible with an extra page in it, including a mud map of Cait's location in the galaxy). Presumably, there were plans to include these details in a TAS episode if a script ever required it.
Call TAS names silly, but similar naming precedents on TOS go back a long way, such as Helen Noel (at the Christmas party), the forgetful Lethe, Romulus and Remus being brother planets, and Mr Atoz (A to Z) the librarian.
I have no problem with humans originally giving Caitians and Triexians anglicised names that the Universal Translator then repeats whenever a Caitian or Tiexian states his home planet name in his native tongue.
However, Arex's people were never named in that TAS bible, and thus Bjo Trimble didn't include the species name in her "ST Concordance". If PAD used the writers' bible or the Concordance for his research, he had nothing solid to go on.
Arex's home planet, Edos, is mentioned only in places like the "ST Logs" episode adaptations, the bio of Arex sold by then-Lincoln Enterprises, and Bantam's "ST Maps". Nothing canonical. PAD may well have avoided using Edos since TNG had its own Edo. Sly references to "Edosians" come from places like DS9 and ENT scripts, but it's only fan knowledge that links such references in our heads.
In any case, I love the explanation in "The Road to Edos" ("No Limits") about the differences between Edoans and Triexians, and the frequency of people confusing the two races. (I'm sure Triex is a an old Edoan colony world.)