N501MR is reserved. Post-cancellation hold held by Cancelled/Not Assigned — if it isn't renewed, the FAA releases it on Apr 1, 2029 (in about 2.7 years).
This tail was recently cancelled. The FAA holds cancelled N-numbers before releasing them back to the public.
Reservations lapse more often than you'd think. Check back around Apr 1, 2029 — if the holder doesn't renew, it becomes available. See everything scheduled to free up in April 2029.
N501MR has been worn before. Past registrations from FAA deregistration records:
Tails one nudge away from N501MR that aren't assigned or reserved: