This is something I have been curious about. We all know the books are not offically part of canon or the tv continuity. If this is the case then I always kind of wondered why there was/is a need to try and stay consitent with the tv shows?
The purpose of tie-in novels is to give fans of a show more of the experience they get from the show itself. The books exist to support the show and follow its lead. Also, the licensors generally prefer to avoid confusing the readers by having the books conflict with the onscreen continuity. Even if they aren't actually binding on screen canon, it's preferred to keep them consistent with it as much as possible, to supplement it rather than clashing with it.
If the books can't impact the shows then why not have Kirk die in a book ro hook up Picard and Crusher in a romance?
Actually, now that the shows are off the air, the books have much more freedom to make changes. Picard and Crusher are married and expecting a son. Riker and Troi have given birth to a daughter. Kathryn Janeway is dead in the book continuity, and Trip Tucker's death was revealed to be a hoax. Kirk died onscreen, but was resurrected in the novels co-written by William Shatner. Books based on an ongoing series are expected to follow its lead for the reasons I mentioned above, but books that are carrying the torch on their own after the end of the series they're based on have a much freer rein.
Sort of like those old "Quantum Leap" books. Does anyone recall them? In the books Sam was literally leaping into people's bodies, were as on the show he simply looked like the people who he has displaced.
The science and logistics of
Quantum Leap were so nebulously and inconsistently defined on the show that the authors of the novels had to take liberties. (For one thing, if it was Sam's body and others just saw an illusion of the leapee, then how come their clothes always fit him?) It's true, however, that Ashley McConnell's interpretation of the QL universe was somewhat different from that depicted on the show. But that's because the books were from a different publisher and under the supervision of different licensors. Not all tie-in books follow the exact same policies and practices because they're not all from the same people. Different companies, different creators, approach their properties in different ways. And isn't that the way it should be? Where would be the joy of discovery in reading if all storytellers followed the same rigidly defined set of rules?
Star Trek continuity is so well-known, so detailed, and so religiously studied by so many fans that the guidelines on following it have to be fairly strict. You can't play too fast and loose or audiences will recognize that you've got it "wrong." Of course the various tie-ins aren't always compatible with each other, but they all have to have a common starting point, the shared touchstone of the screen canon. Authors adapting a show like QL, with a more vaguely defined canon, can have more luxury to add their own interpretations -- and indeed, if you look at early Trek novels from the '70s and early '80s, you'll see that their authors often brought their own idiosyncratic interpretations to the universe, because it wasn't as clearly defined and detailed back then as it is today. So it does depend on the franchise, and on the approach of the publisher.
Also, audiences have gotten more demanding over time. With the rise of home video and the Internet, access to the original source material has improved and fans of TV and film series have gotten less patient with divergences. Film and TV novelizations in the '50s and '60s often diverged wildly from the source material, heavily rewriting it to work better in prose or to suit the author's preferences and style. (See James Blish's earliest TOS episode adaptations, for instance. Or Isaac Asimov's novelization of
Fantastic Voyage, wherein he heavily rewrote the story to fix the bad science and make the hero more intelligent.) Today, novelizations and tie-ins are expected to be much more faithful to the source material because it's so easy to compare. The
Quantum Leap novels came in the '80s and '90s, in between those two extremes, so audience expectations were probably looser at the time than they'd be today. (Ashley McConnell went on to write some
Stargate SG-1 novels, and I believe she took similar liberties, but her books were not as well-received by fans as the current SG-1 novel line from Fandemonium Books, which is more faithful to the show.)