Yes, a zero for page number sounds like a good idea if reviewed recipes is from an Ebook with no page numbers in it. That would be a way to flag other folks to enter it, if they want to, from their hard copy. I sure wouldn't mind going through my books looking up page numbers to insert into someone's review if I have the book. Sounds like fun and would help a bit to justify keeping TOO many cookbooks in my bulging house.
My original reason for wanting a way to identify an Ebook vs Hard Copy was for myself--for my bookshelf. I have lots of both kinds of books (HC+E) and I would like to have something listed that could tell me WHICH version of the book I own...one reason: it would serve as a road map telling me where to go look for the book in my stuff (like when I want to go look up the recipe) that somebody has just raved about. :)