Bingowings said:
The whole Episode IV thing since the early eighties sort of makes a trilogy an all or nothing proposal.
Lucas has changed the movies so many times, he could have did away with the episode numbers altogether in the late 90's.
If you remember, even the 1997 VHS Boxes on the sleeve did not contain the Episode #'s, as they were just Star Wars, Empire, and Jedi. Lucas didn't start putting episode numbers on the sleeves of home video until the Episode I DVD came out. In fact, I remember leading up to the opening of Episode I, he actually called it Episode I for the first time, as he never did that in the 80's. They didn't advertise Return of the Jedi as Episode VI, they advertised it as Return of the Jedi. Or Revenge of the Jedi in 1982. ;-)
Heck, Lucas made Luke and Leia siblings after they smooched, he could have easily deleted the episode numbers from the movies and just released one prequel movie and he would have been fine.