Weren't Mosaic and Pathways briefly canon to voyager before Jeri Taylor left? (falling therefore along the same lines as the B5 works)
Well, sort of like the B5 works in reverse. "Canon" just means "the work of the creators themselves," and when the creators themselves write books (or outline them, in JMS's case), then they're generally canonical (unless the creators don't intend them to be -- I don't think the jokey Ferengi books that Ira Behr wrote were intended as canonical per se). But when the creation is passed from one person to another, as when Taylor left VGR and Brannon Braga became showrunner, then a different creator is in charge and the ideas of what's canonical can change.
Basically,
Mosaic was written while Taylor was in charge, and she used elements from it in "Coda." As far as I know, the remainder of the TV series didn't directly contradict it in any way, though I'm sure they wouldn't have hesitated to if they had reason. Taylor presumably intended
Pathways to be the official word on the other characters' backstories, but her successors on the show didn't consider it binding and the tie-in authors weren't expected to either. So pretty much every character-bio flashback chapter in
Pathways has been contradicted by something in canon or the novelverse, except for the Kes chapter, since once she was gone, the show didn't reveal anything more about her past anyway. (Chakotay's flashbacks were contradicted by Christie Golden's novels and
Tales from the Captain's Table story, with regard to which Captain Sulu sponsored him and what his family makeup and history were like. The names of B'Elanna's parents and the planet where she was raised were contradicted by the show; I think
Pathways called her mother Prabsa instead of Miral. I think Harry's Academy flashbacks in
Pathways don't quite reconcile with the whole Lyndsay Ballard business in the show. And so on. I don't quite remember all the inconsistencies I noted before.)
EDIT:
Idran has a point -- the Taylor novels probably weren't intended as canon per se, because they were merely a supplement to the show, secondary to it. Generally, creator-written tie-in books and comics are only "the canon" when the show they're tying into is no longer in production and the books/comics are the only form in which the series is continuing. As long as you have both a show and books at the same time, then the show is the primary work and any books, even those by the creators, are supplements. (Assuming that the books are based on the show and not the other way around. In the case of something like
Game of Thrones or
The Expanse, obviously, the books are the primary canon and the TV shows are adaptations thereof.)
And, I did hear that the much returned to All Good Things future was implicitly designed around being that from the Imzadi novel, though as both versions of that future end up being erased by temporal intervention, or may have been a Q pocket universe, it's somewhat moot.
No, that's not true. The details of the two futures are rather different. The only points of commonality are that Riker is an admiral and Deanna is dead in both futures. But in
Imzadi, Deanna died during TNG's fourth season (2368), while in "All Good Things..." it was an unspecified time after 2371. And Riker is in a dead-end starbase command in the novel while he commands a modified
Enterprise-D in AGT. In
Imzadi, Data is captain of the
Enterprise-F, while in AGT he's a Cambridge professor. Also, Wesley is captain of the
Hood in
Imzadi's future, while AGT was written after Wes had gone off to be a Traveler. True, the AGT future is c. 2395 while
Imzadi's is c. 2409, and
Imzadi doesn't mention anything about Picard, Worf, Beverly, or Geordi that would contradict AGT, so maybe you could fudge most of it if you really wanted to, but the Deanna contradiction is pretty much irreconcilable, and having Wes return to Starfleet would be a real stretch. So while there are a couple of coincidental similarities, it's clear enough that the writers of "All Good Things..." had no intention of evoking the
Imzadi future. They'd probably never even read the book,
any of the books, since they were too busy making the show.
The thing is, different creators accidentally come up with the same ideas all the time, especially when they're working with the same series and characters. With the same ingredients and initial conditions to work with, parallel evolution is bound to occur from time to time. The number-one reason why TV episode pitches get rejected is "We're already doing a story like that." So if anything, writers have to try hard to
avoid coming up with similar ideas, and thus it's most likely for two works to resemble each other when their creators have no idea of each other's plans. But laypeople don't know that, so when they see a similarity between two works, they assume it was intentional.