Multiple "copies" of audiobooks in iTunes

I am using iTunes on Windows 10. There are multiple "copies" (air quotes) of most (not all) audiobooks in iTunes. I used air quotes because when I search the PC for the books, there are only single instances. Another post (https://apple.stackexchange.com/questions/64097/why-does-itunes-create-multiple-exact-copies-of-my-music-files-and-hide-them-fro) asked a similar question about music files. The answer for that post alluded to a playlist problem. But (a) I do NOT have any playlists for my audiobooks, and (b) that post is old, dating to Sept. 2012. I am running version 12.7.2. When I select a copy of a book and drag it to my iphone, I can see that the copies are numbered 1, 2, 3, ... When I try to delete any one of those copies, then all copies are deleted. What can I do clean up the lists so that I only see one copy of the book?