Well, in this case you really need to know more about the authors actual intentions. It could refer to several "books/registers", i.e. as you say it could be a book with a registry => "Registry book" it might also refer to an open "book" intended to be used for continued 'signing up' and/or registrations => "A registration book" - It could also refer to a "Book of records", registrating almost anything. Last, I believe this is not an ordinary book at all - instead a computer registry/record of some sort.
If I would specify it more in detail my suggestion is to use the word "Registry" since this has a broader meaning and will cover most interpretations mentioned above.
This is a listing of 1970 Mustang Mach1 owners and actual condition of each car registred in this Registry: http://www.homestead.com/1970mach1/home.html