Well, George still talks as if he has had the stuff you see in ROTS in his mind now for 30 years. I've not really heard him talk about having the first two in his mind, except the idea of the 'Clone War'. As he said, a marketing firm would have told him to start the prequels with ROTS and then fill in the next two films with the 20 years between the films. That's not the way he wanted to do it. Well, hats off to him, even if the story would have been better the other way.