People call these things fanon: "fan canon." Though given the adjective form of canon is canonical, surely they should call them fanonical... no? Okay.
- No one on the original series ever actually described Spock as the first Vulcan in Starfleet.
- Circumstantial evidence is against it. In "The Immunity Syndrome," we learn of (though we do not see) the USS Intrepid, a starship with an entirely Vulcan crew, numbering 400. It seems somewhat unlikely that all 400 Vulcans could have joined Starfleet after Spock, especially given at least one would need to be of higher rank.
Recently this happened again, and I was surprised to realize that the thing to become canon was not in fact already canon. Season 2, episode of Star Trek: Discovery, "New Eden," mentions "Federation Standard" as the language the main characters are speaking. Something I did not realize until logging onto the Internet after watching was that it was the first canonical reference to Federation Standard. But I just knew-- had always known-- that the language was called Federation Standard.
A little bit of research, and I'm still not exactly sure where the term came from. It was being used in novels in the 1980s, which is probably how come I assimilated it.
What I wonder, though, is if the writers of Discovery actually knew what they were doing when they used the term. Did they know they were "canonizing" a long-standing piece of fanon at long last? Or did writers Vaun Wilmott and Sean Cochran think, like me, that the term already was canon, and thus inadvertently made it so?