Creating unique identifiers while having access to a global db of all previous unique identifiers is not really the problem uuid is trying to solve most of the time.

Each bitcoin is identified by a block assigning it to a key. Keys are not guaranteed to be unique, with enough guesses you can duplicate one (if you have some time before the heat death of the universe or so) and maybe win the lottery (i.e. access to someone else's bitcoins). So in all, things are more "very probably unique".