Uncut refers to pages that are rough or uneven. Untrimmed. Think deckle-edged.
Unopened refers to the book's pages at the fore edge and/or top that are still joined from the folding. Back in the day, many books were issued unopened. Men used to carry a paper knife ( in some sort of protective sheath, I hope) to cut the pages in such books. Today we would call such a tool a letter opener which is just what I used to carefully open the pages.
I guess this means that the original owner of the book did not read all of it. That is a shame for I find it engrossing.