Comment by stanmancan

Plenty of systems end up generating multiple UUID's in a single millisecond.

The issue with UUIDv7 is that you also have significantly less entropy since you only have a 62 bits (sometimes less, depending on implementation) of "random" data. So while the time aspect of format lowers the chances of collisions, generating two UUIDv7's in the same millisecond (depending on implementation) have a significantly higher chance of collision than two UUIDv4's.

It's still incredibly unlikely, but it's also incredibly unlikely you generate two matching UUIDv4's, but it does happen.

TLDR; It's possible to generate matching UUIDv7's, don't assume otherwise.