This question already has an answer here:
Having just re-read the A New Hope novelization (credited to Lucas but ghost-written by Alan Dean Foster), I was struck by how different it is from the movie in several places (mostly dialog, but also some cut scenes or scenes in a different order). Further, it's a printing from the Special Edition era, though it appears to be the original text and not updated in any way.
I've read Disney considers only the six (er, seven) movies, the two animated series, and new books to be considered canon. It doesn't appear there's much in the way of levels of canonicity other than "canon" and "Legends."
I believe I've also read (but now can't find it, so I may be mistaken) Disney considers the prequel trilogy novelizations to also be canon.
So where does this leave the OT novelizations? Especially where significant differences may exist?