I ran across a couple of Generations scripts while straightening my library. Forgot I even had them.Yup, exactly this. I've got every draft of Generations in my collection, and the overall shape of the script really doesn't change from draft to draft. Individual scenes changed slightly, dialogue always changed, and the fate of Lursa & B'Etor dramatically changed, but the large brushstrokes were locked in.
All Good Things had more adjustments to its story structure in the two-ish months it was being written.