positronic,
I'm not an expert either, but. There are two issues, PD - Public Domain and Copyright.
Something is PD if nobody claims ownership of it and it is also out of copyright.
So for example, nothing here from DC, Marvel, Disney or King because all of their stuff is under constantly renewed copyright. I believe the cut-off date for PD is 1964. There are many posts on CB+ re Copyright and PD
It's complicated.
However, the internet being what it is, If you search hard enough, I am sure you will find the books you would like, on other sites. Just not CB+
cheers!