Cannot import different versions of iBook

My students have made their own iBooks from a single iBooks Author template that I made for them. Their work has been exported to iBooks files. I cannot import their books into iBooks on Mac or iPad.

I can import the first book no problem. However, when I try to import a second one, iBooks just opens up the first book I've imported. In order to update a new book (or an edited version of the first book), I must first DELETE the book from iBooks.

I would like to import all of my students' books into my iBooks library, but can't seem to do it.

I have a feeling that iBooks is reading each new book as the SAME book and just opening it, but I don't know why or how to get it to see each book as unique.

Any tip? Thanks!

Rob