...one volume doesn't mean that I've only read one book. Otherwise I could get them in three separate volumes and call it three books, or read them collected into one volume and call it one book, even though it's exactly the same text. Which would be absurd. We have the entire works of Jane Austen in one collected volume – does that mean she only wrote one book?

So, for example, if I had read all of Lord of the Rings in a single bound volume last year, that would be three books, even though it calls itself six books, because it was three separate publications.

I did, in fact, borrow a single volume of the Illuminatus! trilogy, but it's still three books.

(I don't know if you were asking me, but I answered anyway )