I had my shot yesterday, so I was a little apprehensive about today...which went fine from a productivity standpoint at least. I input the final corrections from two days ago, and then I proofread the layout through Chapter 20.
The problem was, what is now Chapter 20 used to be part of Chapter 19 (which now contains some of what used to be Chapter 18). I've been going back and forth on where exactly to break those chapters for a bit, but reading it today, I realized that I had a long chapter with a internal break, and in the course of the break we 1. change locations, 2. fast-forward through some action, and 3. change narrators. I decided that was really just too much for an internal break to handle, and that I had to make a new chapter.
Honestly, it is late in the process to make that kind of decision: It's added a page, meaning that from Chapter 20 on I'll need to change chapter numbers and page numbers (including turning left-handed pages into right-handed pages, and vice versa), and adjust how the newly-facing pages relate to each other. Let's just say that, if I were a publishing house, I probably would not be fixing this. But I think I can manage it without delaying sending things to the copy editor by much--and luckily I can delay my next shot until Tuesday if I have to.