Bruji

to be able to create a smart collection that shows me books (bookpedia) that are only in a specific collection and no others.
(Such as "what's in the library and has not been put into a collection yet.")

That could be an interesting smart collection. Thank you for the feedback. Depending on the number of collections you have, you could set it up with a number of rules: "is in library and is not in first collection And is not in second collection".