I'm so sorry whitewoods - somehow I missed your question. You cannot see which books were manually added for the entire Library. Though you can reasonably assume that any newly added books in the Library that are not new or upcoming books have been added by members either using Import Books or the new Member Added Books feature.
You can view the books that you added or tried to add using Import Books. Click 'My Added Books' under the My Bookshelf tab. You can then select three filters on the right of the green search bar - Imported (all the books you personally added to the Library), OnAmazon (books you tried to add but could not import as Amazon had neglected to add a food or drink tag), and NotOnAmazon (books you tried to import but could not as Amazon does not list them). Any of the last two categories can now be added to the Library using the new Member Added Books feature.
You are correct about Spiralize It! - it could not be imported. But when LLuAnn added it manually, it also got added to the Bookshelves of any other member who had imported the ISBN in the past.