Exactly. I have nothing against making up story parts as you go along. If you manage to do it well, it can come across quite seemlessly. Like the OT for the most part. Another example is Back to the Future Part II, where they never wanted to go to the future, but they were stuck with the gag ending they had written for the first movie. So they took that and let that springboard them into another plot about time paradoxes. Just the fact that the PT has "forced" George to go back and actually change the original movies to fit it is a testament to how poorly they were conceived.