Nine Versus Twelve

Two nodes use Lamport timestamps. An event on node A carries timestamp 9 and an event on node B carries timestamp 12. What can you validly conclude about the relationship between the two events?

A's event happened earlier in real time, because both counters advance once per local event

Nothing about causality: a smaller number does not imply happens-before, so they may be concurrent

A's event happens before B's event, because Lamport timestamps are always consistent with causal order

The two events are concurrent, because they were assigned by counters on different nodes