When the OP says "They were very well packaged and protected both times." I am not sure what that means. How about a picture? Books are liable to get damaged in shipping if not packed carefully. I recommend double-boxing if not triple-boxing on stuff you really want to be safe.
I had a USPS Priority mail, double-boxed, CGC book sustain heavy damage to the box resulting in a cracked case. Fortunately, the book was not damaged and only needed a reholder. I think USPS paid the insurance without me having to go into the Post Office or surrender the book.
Looked something like below:
If USPS made it too easy to claim compensation from damaged mail, that would open them up for excessive fraudulent claims