Now that I'm into the second part of my novel rewrite (i.e. 'Act 2') I'm finding there's quite a high proportion of material that's to be retained. Or at least I plan to retain it at this stage . . .
It's an interesting process. At the end of the previous complete draft I spent quite some time going through scene by scene, making a judgement as to which scenes needed to be deleted, which edited, which rewritten, and also some to be inserted as well. I knew Act 1 required quite a deal of rewriting and new scenes, because the setup is so very important. Even so, I believe I've rewritten more than I originally intended. It will be interesting to see what happens with Act 2, where much of it was deemed OK upon first consideration.
The tricky thing is this: On the face of it, an existing scene may read really well. It may convey essential ideas, setting, backstory etc. But what happens when you change the scene preceding it? Suddenly, your characters are in a different place emotionally and possibly in other ways as well. So you need to carefully retrofit these moods & thoughts & repercussions into what's already there. But if you're already more or less happy with what's there . . . the whole thing can fall apart. Or else you kid yourself that maybe X wouldn't be dwelling on a specific event just then and so you ignore it. (And in many cases this would be true!)
When you're writing as sporadically as I am, it's very easy to 'forget' where your character is emotionally. This is why I always read back over what I was last writing, rather than launch straight into new words. I have to get back to the right emotional place. Plus in addition to emotion there are so many other things to keep track of: adornments and accessories, knowledge gained and mulled over, rising conflict . . . so many issues! This is one reason why I think I have a tendency to rewrite more than I intend. That, and I always find myself second-guessing the quality and appropriateness of the existing scenes. Surely I could do a better job if I rewrote it in such a way? I find it hard to judge sometimes just how 'right' a certain scene is.
When does an edit become a rewrite? I find this an interesting question, because so often I slip from one to the other without really noticing. There's a 'place' where you start with a scene, retain/edit large chunks/sections at a time, while simultaneously writing new chunks to replace the chunks that have been deleted. I honestly don't know if that's a rewrite or an edit.
In any case, although I invariably think such a modification ends up better now, who's to say I won't come back to it in another few years and think it's rubbish? It would be so much better if I rewrote it this way . . .
I guess you just have to keep going and make sure that the story feels right. So if an edit slips into a rewrite, you just go with it. In the end it must be better. Mustn't it?