Many things are published without ISBNs or have ISBNs and aren't traditional books. Here in China, to get an ISBN for a book you have to have a government approval process. So many publishers will print stuff on the proverbial sly, often at night, without assigning an ISBN. There's also book-like printed matter (pamphlets, maps, posters, puzzles, 3D/fold-out dioramas, etc.) which often lack an ISBN. So equating ISBN with book is not correct. Then there's all the stuff published pre-ISBN...