I have two possible clues:

The first is partially a lyrical clue. In the song "Rain" (from Past Masters II), the ending is played backwards. Could this be a clue to start listening to the music backwards?

The second is an album cover clue: On both Rubber Soul and Revolver, the words "The Beatles" or even "Beatles" aren't present on the front cover. I know Paul supposedly died after Revolver, but maybe it was before that, and they didn't feel comfortable being called "The Beatles" without Paul.