Tapes can also fail to reclaim in you have RESTARTABLE RESTORES hanging
around.

In this case you will find in the server actlog:

 ANR1089W Space reclamation terminated for volume xxxxx  -    lock conflict.

From a server command line, do Q RESTORE.
You will see there are some restartable restores hanging around.
When the users finish them, or their timer expires, the tapes will go ahead
and reclaim the next time reclamation runs.