Why are we sharing only 2?

Interesting - I've been keeping an eye on the shared books and we seem to have 'Noah's Arc' - two of each kind.
Also interesting is the lack of Detectives!

What a strange thing.

I know that at least two of us own The Big Sleep but it's not showing up under shared either.

Different editions I wonder?
We've made it to three with a detective! (Athenian Murders).