given the option to remain anonymous
Well, they could do that simply by not writing their names along with their note.
I think simply stating clearly on the book’s cover that its contents may be “reproduced and/or published” is adequate. People can then adjust what they do or don’t feel comfortable writing as appropriate. I do not want to get us into the business of determining which entries we can or cannot reproduce based on a check mark.
That way there is an implicit expectation that anyone anywhere may read what is written, much like the log books in the huts.