I'm tending toward zombie's hypothesis in The Secret History of Star Wars, that Lucas fully intended for "Revenge" to be the title until the final change. I know that there was that one "Return" mention from '80, but I can't really buy that "Revenge" was a fake-out title. Secret History goes into full explanation of how the "Revenge" title goes all the way back to 1979. "Return" *may* have been kicked around early on, but Lucas obviously settled on "Revenge." Until Lucas and co. got second thoughts, "Revenge" was the real title.

The "it was originally called 'Return'" spin goes back to '83. For example, when Nickelodeon's "Standby, Lights, Camera, Action" had a segment on ROTJ, the film had already been retitled, but the documentary footage they showed referred to it as "Revenge of the Jedi." Leonard Nimoy explained that "Revenge" was the working title, but repeated the Lucas spin that "Return" was the original intended title. (And I'm not sure if the film was even out yet when this aired!)