The spec doesn't assume that a 30040 is a book, that's why it's that way. It could also be an index of articles or wiki pages from different authors. Or pages from various books from various authors in various editions.

That's why only the title is required, as everything has some sort of title. 

 I like #1, for cases where the lower-level stuff doesn't have their own tags.  I had to do this, when I ran into the problem that I had two different editions of one audiobook and they kept overwriting each others' events, even though I changed the version of the 30040.