As a writer and an avid reader, I think that the word of the author should hold weight in the interpretation of the work. I don't think that there is a time limit to how long afterwards an author's interpretation of his own work remains valid. Tolkien's word should still be the primary influencer of any interpretation of Lord of the Rings, for instance. The exception to this is if what is obvious in the text contradicts what the author is saying. This could be a failure to execute his idea on page or screen, or it could be retroactive editing, but in either case it can be ignored. There are, of course, differences between a static work (a novel, a movie) versus an ongoing work (a franchise.)