> by generating more than 2^B UUIDs on the same machine within a fairly short timeframe and fairly large B
Which can be made impossible.
IDs are part of the finite system and don't exist on their own. And the system can perform a finite number of operations both concurrently and in a finite time-interval with some amount of uniqueness distinguishing nodes and other useful properties. Making it possible to always find an id generating algorithm for this system that can never have collisions.