Unique id

I know this one is old as the hills as I have been trying to research it on the forum, but I just have a general question about the universal Id.

Lets just say hypothetically that I have one database with one billion forms saved to it, would the universal Id be unique for those one billion forms, in other words does it ever overlap or will it always produce a unique Id for all docs in that one particular database.

Subject: unique id

A UNID is always unique in a database. It would theoretically be possible to run into must-duplicate problems once the database has accumulated 16^32 (or 3.4028236692093846346337460743177 x 10^38) documents, but I don’t know what kind of system you’d keep that NSF on.