Did you check the styles? Style names are case sensitive, among other things. Be sure you have the correct included styles assigned to all of the chapter entries you expect to see.
Thanks so much for your response. I did verify that all of the styles match
in both case and definition. I even went so far as to load the styles from
one of the files that does appear correctly in the TOC to one of the files
that is missing from the TOC, saved the files, synched the book and saved
the book, recreated the TOC style ... then generated the TOC - and the
outcome remains the same.
Any other thoughts?
Might be time to rebuild the book. Export ALL of the individual files to .idml, save new .indd files from those, create a new book and add the new files, then make a new TOC style and add the styles to it, and finally make the new TOC.
Will give it a try - fingers crossed! Thanks!