Most of the NDAs I have to deal with (industrial/aerospace) have clause that anything that is "public knowledge" falls outside the NDA.
Since the Beginner Boxes have been sold to the public, and people have been posting pictures of the contents, I would say you are now in "public knowledge" territory, same as the Streetpedia. I don't think you'll be able to discuss the core book, but any rules contained in the Beginner Box should be fair game.