Hi Jim,
The values are still globally unique. The odds of a collision are very very low. Two instances with the same node_id generating on the same millisecond (in their local view of time) have a 1:2^34 chance of collision. node_id only repeats every 256 machines in a cluster (assuming you're configured correctly), and the probability of the same millisecond being used on both machines is also low (depends on generation rate and machine speed). The only real concern is with clock replays (i.e. something sets the clock backwards, like an admin or a badly implemented time sync system), which does happen in rare instances and is why seq is there to extend that space out and reduce the chance of a collision in that millisecond. (time replays are a real problem with id systems like snowflake.)
Also, the point of the timestamp isn't uniqueness, it's the generally monotonically ascending aspect I want. This causes inserts to append to the index (much faster than random inserts in large indexes because of cache coherency), and causes data generated around the same time to occupy near nodes in the index (again, cache benefits, as related data tends to be generated bunched up in time).
Thanks,
-Cliff.