I got through to the end of the book. Part of it actually brought tears to my eyes. I guess that's a good sign. I was quite taken aback.
I have a list of knotty issues that have to be integrated with other knotty issues. As we reach the end of the book it's harder to discuss anything without spoilers. I think it's safe to say that there's a point where I and some characters made a decision about who would participate in the resolution of the book. I made a note about giving serious consideration, as I read on, as to whether this decision was right or not. Then I read on, and was actually so pleased with the resolution as it stands that the idea of adding even one more person to the complicated interactions already present was very unwelcome.
I do not believe that "kill your darlings" is useful advice for writers, so the mere fact that I really like the ending as it stands is not an argument to rip it up and do something else. I'm still concerned with the amount of participation provided secondary characters, for Reasons.
I also realized that a lot of the second half of the story consists of research and quotations or summaries of information found in books. These passages were a lot of fun to write and I will probably let most of them stand. People who read books about magical libraries have to expect a lot of this kind of thing. However, in the case of at least two characters, one of them still extant in some sense, I wondered if it would be better to tell a few threads of history from their viewpoints as those events happened, rather than summarizing them from the viewpoints of contemporary characters. Doing this would not rip up a complex structure to the degree that adding supporting characters to the resolution would, but it would be an interesting structural challenge. Ideally, accepting said challenge would in some way or another resolve some of my other difficulties. I can't at the moment see how this is likely to happen, but I've been surprised before.
My next step, now that I've hardened myself by reading the entire book through for the first time in some years, will be to drag out the massive manuscript scrawled over with my notes from the critique session my writing group as it was then constituted did for me. Some of their remarks stayed with me without any need to refer to my notes, and I've kept those in mind and discussed some of them in these posts; but there are bound to be a few nasty surprises in the notes.
I'll let you all know about that next month; with any luck, before the very end of it.