It would explain why Ione can't find books of comparative theology either.
It also sounds an awful lot like an excuse.
And if the Conspiracy isn't trying to deliberately misdirect Keltham's attention - and they weren't that clever, at the first point when books of comparative theology started not being in the archduke's villa - then it implies that the Conspiracy is trying to hide something about afterlives, gods, and theology.
Keltham will take the standard set of Church books then.
On to fiction. What's has the proprietor got with magic, gods, afterlives, people going to magical academies, mysteries that hinge on facts about magic or at least involve technical discussion of those, people going to afterlives and coming back, a character goes to a temple for training at some point, romance novels with Chelish protagonists or love interests -
...also anything that would be. Like. Fun to read if you had high Intelligence and Wisdom. But that's a separate question so long as he's here.