Right. This presumably is also why library e-book collections contain a finite number of "copies" (licenses) of each book, and if all those copies are checked

Right. This presumably is also why library e-book collections contain a finite number of "copies" (licenses) of each book, and if all those copies are checked out, anyone else who wants the book is put on a waiting list. They're allowed to loan the copies they've paid for already, but not to make additional copies.