Giordano, thank you very much for taking so many hours to research my questions.
May I also suggest the legal experts consulted by the Anne Frank foundation are being very liberal with the statement " We have concluded that the editing, merging and trimming of entries by Anne's father " created a new work" worthy of its copyright." He merged them he, cut them and he changed them, so he created a "new book"
I would answer the above:-
A) A diary is a very personal possession, it can never be created in to a new book with co-authorship by a third party.
B) Legally unless a book has been changed very dramatically it can't be co-authored, otherwise all editors that merge and trim an authors words can be credited with creating a new book.
The Rebel.