N9231E is reserved. Post-cancellation hold held by Cancelled/Not Assigned — if it isn't renewed, the FAA releases it on Dec 14, 2029 (in about 3.5 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 Dec 14, 2029 — if the holder doesn't renew, it becomes available. See everything scheduled to free up in December 2029.
N9231E has been worn before. Past registrations from FAA deregistration records:
Tails one nudge away from N9231E that aren't assigned or reserved: