Originally Posted by
Zero
The thing is, there is NO statement that they are NOT canon, while for other medias, like games and movies, there was one regarding them not being canon (if Kubo wasn't ok with the stories in them, then he would put a statement regarding them not being part of the official story). Beside they explain the state of things that are currently present in the manga, yet weren't before the time-skip, like Ruki'a new hair style and etc.
Well, they are only semi-important, to the point that they currently do not have much impact on the story. If they didn't exist, the story wouldn't change much anyway, so there really isn't any problem. It was meant to widen the Bleach world and make the story deeper. Plus it's not like there weren't any other Bleach Light Novels before the "Missing Link" project.
What's more, I saw other manga series that had beside them additional light novels, like D.Gray-Man, and those are considered canon.
Basically, as long as there is no mention of them not being canon, they are considered canon. Especially as the books were printed awhile ago and they would have a certain sentence in them if that sentence was needed (for example at the end, postscript etc.).