It is a combination of expiry and reclaimation which will free up your offsite tapes.
Some good reading on the topic here - http://www.tsmtutorials.com/2013/03/how-to-reclaim-offsite-tape-volumes-in.html
Cheers
Some good reading on the topic here - http://www.tsmtutorials.com/2013/03/how-to-reclaim-offsite-tape-volumes-in.html
Cheers