Well I guess what most people mean by canon is whether or not those events happened in the Star Trek universe
Which is ultimately for the creators to decide, not the fans. I mean, sure, we can choose to accept or disregard anything we want in our personal continuities, but that's not going to have any effect on what the creators of future Trek productions choose to do. If the writers of
Star Trek: Discovery wanted, say, to do an episode featuring Starfleet Cadet Arex or M'Ress, or Carter Winston or the Vendorians, or the Delta Triangle or the Skorr or the Vedala or the Dramians, they would be perfectly free to do so. Absolutely nothing would prevent it. CBS fully owns every concept and character from TAS (with the exception of the Kzinti, Slavers, and other Known Space elements from "The Slaver Weapon," which belong to Larry Niven), so they're completely free to use them if they want to.
Which is why the unending fan arguments over TAS's canon status are such a complete waste of time. Canon, by definition, is what the creators choose to do. And Trek creators have been including at least minor elements from TAS all along, from the implicit Caitians in
The Voyage Home to the "Yesteryear" allusions in "Unification" (which came out
during the time that Roddenberry's supposed "TAS ban" was in effect, proving how toothless it actually was) to the
Klothos in DS9 and so on. All the fan battles over TAS's "canon status" have no bearing on the fact that the actual makers of canonical
Star Trek have been treating TAS content as fair game the whole time. Roddenberry was the only one who wanted to exclude it specifically, and by the time he imposed the "ban," he had no real power to enforce that preference anyway -- except on the tie-ins, ironically enough, and that was only for a few years.
