Question

Asking questions about monographs

Answer 1

Well if they find it rude they won't respond, so no harm no foul. I'd suspect that they would actually like to receive questions on a topic that they are/were clearly interested in, enough so to write a book on it. I'm not in research currently so I can't speak from experience, but I've heard about and spoken to people who have written to authors of texts and relevant researchers in a particular field. It couldn't hurt to try.