The making of Empire book clearly puts Guiness on the set during production of that film. (For ESB, he shot all his scenes in front of a black background.) The interview for that book mentions his annoyance at not getting residuals for a lot of his early films, which was probably a factor in getting a slice of Star Wars pie! The book also mentions how George wanted to have all the Dagobah scenes for Jedi shot during production on Empire, but ran out of time.