I think I would try farming email addresses and license history via
QRZ.COM and if they don't have a reference to an email or active
callsign simply delete the assignment and DNS. An expired call implies
a changed call or SK. Second level, assuming they passed the valid
call test, would be a ping test to the allocated IP or a post card.
But I'm not inclined to spend a lot of time or money on it.
Tedious, but it can be done.
--
Geoff Joy - ke6qh -
AmprNet IP Address Coordinator for San Bernardino & Riverside Counties.
geoff(a)windomeister.com