I am misunderstanding the problem you are trying to solve. Books need tags, not chapters. That's what collections are for, is it not? To group similar books together in any way you wish? You can organize them with any labels you want, even if they overlap. So a story about a winy teen from the 1940's who falls in love with a girl who is murdered could be in the following collections: Mysteries, WWII, YA, Books where the lead is unlikable, Romance...
For me, I just use four collections: Unread, Reading, Read, Ignore
Yeah, you are fundamentally misunderstanding the problem again. How does the Books app know
which book is
which? It uses the tags
inside the files.
Let's say you've been given the CDs of The Hitchhiker's Guide to the Galaxy audiobook, and you want to listen to them on your iPhone. You rip the first CD, and it has 24 tracks.
Once you've ripped the tracks you need to add tags to them to say that the first file is track 1 of 24, the first chapter, and it's called "This is the story"; the second is 2 of 24, and called "You've got to build bypasses" etc.
You can add this info into the file using the Music app. You Get Info on the first file, go to the Options tab and set the media kind to "Audiobook", then you add the correct tags, the chapter title, author etc.
Then you drop that file into the Books app and add it to a new "HG2TG" collection. You now have a collection with one chapter in it. Back in the Music app you add the tags to the second file, and add it to the collection, and so on.
If you don't add the tags to the files, you won't know which chapter is which when you add it to the Books app.
And, as I have stated previously, you cannot remove an individual chapter from an audiobook because the Books app stores them all under the same title, i.e. when I've added all 24 chapters to my collection, I look in the collection and there is only
one item that can be selected.
Let's say I misspelled "bypasses" in the second chapter, I cannot see the individual chapters until I play the audiobook, and I definitely cannot edit the chapter name to correct the spelling mistake. I cannot remove that individual chapter from the library or the collection either. What I have to do is to remove the entire audiobook from my Books library, edit the tags of the chapter 2 file back in the Music app, then add the entire audiobook back into the Books app.
Understand now? The Books app is a UX nightmare. When we had everything in iTunes we had the ability to edit the tags for every file in our library. Now everything has been split out, Apple have removed the most basic of abilities. The Books app is crap.