JMS was not involved with most of the original Dell paperback B5 novels. When those were being written the show wasn't even on the air in many places, and few of the authors had managed to watch an episode, or even read any scripts. Jeanne Cavelos, writing one of the last books released, was able to watch the show, and to pose questions to JMS. Hers was the first book that he considered "mostly" (like 70%) canon. Not every detail is correct, but the basic story is, and the TV characters are handled appropriately. To Dream in the City of Sorrows was written by JMS's wife - who also wrote an episode for the series - so of course she knew the show very well.
The three recently Del Rey Books trilogies were all based on outlines by JMS, so they are broadly accurate, and he did answer questions by e-mail for all three writers while they were being written and read them all in manuscript. So for the time being they are "canon". But JMS doesn't feel bound by every single detail the writers invented in the books, so if there is ever another B5 screen project, or JMS decides to write a B5 novel himself, he's free to contradict the books. Then whatever hewrites becomes "canon". /forums/images/graemlins/smile.gif
Regards,
Joe