Years ago (as in early 2000s) StarTrek.com did in fact have a "What is canon?" page, though caused contention itself. According to them, Canon was all TV shows and movies (excluding TAS) plus Jeri Taylor's two Voyager novels, Mosaic and Pathways. Meanwhile, at that same time Pocket Books was adamant none of their novels were canon, not even Taylor's.
Voyager itself contradicted Taylor's novels after she left the series rendering them definitely non-canonical anyway,
Basically. Jeri Taylor considered her novels canonical while she was running the show, but her successors didn't follow suit. As for Startrek.com, it was slow to get the memo and kept up the page claiming the novels were canon long after they'd been repeatedly contradicted. And many fans mistakenly assumed that Startrek.com was somehow put out by the producers themselves rather than just being a publicity site run by other people, so its assertions were seen as more authoritative than they actually were.
meanwhile these days TAS seems to have been "grandfathered in" as canon.
TAS always counted. It was produced by Roddenberry and story-edited by D.C. Fontana, it featured most of the original cast, and half its episodes were written by TOS writers. It was as authentic and direct a continuation of TOS as anything has ever been. But it wasn't as frequently shown in reruns as TOS and wasn't released on home video for a long time, so a lot of people didn't see it, and many people dismissed it because it was animated.
By 1989, Roddenberry had become insecure about losing control of the franchise and started asserting that anything he didn't personally oversee was non-canonical, including the later movies and even much of TOS season 3. Although I believe the infamous 1989 memo that supposedly declared TAS non-canonical was really more the work of Roddenberry's assistant Richard Arnold, asserting his own personal dislike of TAS and claiming it was Roddenberry's will. Arnold was in charge of tie-in approvals and prohibited the novels and comics from referencing TAS. But Roddenberry had been eased back to a ceremonial role and had no actual control over the franchise anymore, and Arnold had no power over anything but the tie-ins, so the memo's pretense of "decanonizing" TAS was always a fiction. Canonical Trek did occasionally reference TAS during the time it was supposedly "banned," e.g. "Unification" alluding to "Yesteryear" and DS9 calling Kor's old ship the
Klothos.
It's best to just go with the old rule of thumb that canon is the TV shows and movies, everything else is non-canon. How is that hard to understand? Very straight forward.
More basically, canon is defined by authorship, not medium. At its simplest, a canon is the collective works of the original author as opposed to derivative/imitative works by other authors -- for instance, the Sherlock Holmes canon consists of the prose stories and novels by Arthur Conan Doyle, while all the stage and screen adaptations and prose pastiches by other authors are apocrypha. In the case of a series from multiple creators, like a TV or movie franchise or a comic book series, the "author" is the studio or publisher that releases the series.
The only "canon emergencies" are this, which seems to be the result of someone misunderstanding the terms of the license and/or using buzzwords to grab attention or the situation with the Kelvin Timeline comics, which is well known to be the result of a shady interviewer goading and manipulating Orci into giving a soundbite to fuel clickbait articles.
And even that isn't really an "emergency," just an inaccuracy. After all, canon
doesn't actually matter. Canonical stories are still just make-believe, as much as everything else. It's silly to worry about which unreal story is more unreal than another unreal story. The worst thing that damn '89 memo did was create the false belief among fans that canon is a standard of worth or importance defined by official fiat, rather than just a descriptive term.
