What puts ROTJ ahead of the PT is the brilliant ending. The ads before it's release all questioned whether Luke would turn. In the last half of the movie, he wore all black....referring to the dark side. But then, following his defeat of Vader, the lapel of his shirt is loose, revealing white underneath. When he is near the shuttle with Vader and you, the viewer, know he is not turning...that is when you see the white shirt. It's very subtle, but I'm certain it was intentional, and I think that is just brilliant.