The story may or may not be true, but it’s instructive. Robert Rauschenberg, a painter and collage artist who died a few years ago, is supposed to have sneaked into the houses of people he had sold paintings to, possibly in the middle of the night or when they were out of town, in order to make further changes in the paintings. His work was magnificently chaotic, and the owners might have suspected he had done it even if he hadn’t.
Maybe some works of art can confidently be declared to be finished. Other works, surely not. At the moment I’m working on Book IV of a series of fantasy novels. Essentially the four volumes tell one large story. And fortunately, the first three books haven’t yet been published. When it becomes clear that I misjudged what needed to happen in an earlier part of the story, I can go back and freely apply the hammer and tongs.
I’ve just spent the entire morning making changes in three different scenes in Book II, after which I had to do a quick search in Book III for references to those scenes and do a little nip and tuck where it was needed. I hope I got it all straightened out. Eventually I’ll want to spend a couple of days re-reading the whole story from top to bottom. Not until I’ve reached the bottom, of course, and dredged it out.
The ability to keep a whole bunch of stuff in your head is, I would say, all but essential if you hope to write novels. When I was younger, I don’t think I appreciated that my ability in this area may be unusual.
But that’s only the second half of the process. The first half is figuring out that you need to make the changes. In Book II, Kyura and a couple of her friends are dragged off to the land of the dragons. In Book IV she has to return, more or less voluntarily, in order to solve a big problem. I had originally supposed that the Ribbonglass Tree was hidden in an underground lake in the mountainside city of the dragons, and that the dragons thought the Tree had been destroyed centuries before. That turned out to be a bad assumption. They know it’s there. This alteration has two or three useful consequences, which you’ll have to wait to learn about when the series is published.
Honestly, I don’t know how George R. R. Martin can do it. Trying to write Book VI after Book V has been published? That would give me the jumping willies.