I hadn't really heard of that collection of books but I hadn't really been focused on mystery either, I hope to give this genre a try later on by reading these books that have so much meaning for you.
I think your husband's gesture of understanding what your interests are and doing whatever it takes to recover the lost books is super sweet.
The mystery and detective genre is truly fascinating, and Agatha Christie turned it into a true gem. I highly recommend it to you.