"Unique" is surely an absolute. Something either is different to anything else or it isn't.
So, suppose I have a collection of 100 CDs (and I'm referring to titles, rather than the physical objects). If someone else had 99 of the same CDs in their collection, then mine would only be 1% different, but it would still be unique (obviously assuming that no-one else had the exact same collection).
However, if I again have a collection of 100 CDs and the closest anyone could get to having the exact same collection is to just match with one of my CDs - my collection would be 99% different, and would be unique.
Both collections are unique, but is one *more* unique than the other? If so, surely being 'unique' isn't an absolute but a question of degree. If neither are more unique than the other, how can they both be equally unique if it would only take 1 changed CD to match someone elses collection (and lose the unique status), but with the other it would take 99 changed CDs to match another collection.