Changing the retention period on the policy does not
change the retention period of the tapes that were
already written to. It only takes effect for tapes
written after the change. To modify the retention
period for tapes that have already been written to use
the bpexpdate utility to modify the expiration date or
to expire the tapes completely. If you are expiring
the tapes completely you should also deassign them
from the volume database using the vmquery
-deassignbyid command. That way your volume and media
databases are consistent.

"A wise man once said 'Wherever you go, there you are'"
      -Mike Brady