The command "pmlicense -ud" will return all hosts that have registered with the policy server. Over time this list might become stale if machines are removed.
Over time this list might become stale if agents are removed or decommissioned
The data for registered machines is stored in a file called .lmap.
That file can be safely deleted to reset your license count. Agents will then re-register themselves the next time they communicate with the policy server either through load checks or user interaction rebuilding the list of registered hosts. This process is automatic.