When you start reclaims on a COPY pool where the tapes are OFFSITE, TSM
knows that the tapes aren't available (they are marked OFFSITE, yes?).  So
TSM does the reclaim using only the ONSITE tapes.

If you have 3 tapes offsite that are only 10% good, TSM will mount a scratch
tape, find the onsite copies of all those files, and create a new tape in
the OFFSITE tape pool that is 30% full.  Then it marks the OFFSITE tapes as
EMPTY.  So you send the new tape offsite, and then you can bring the EMPTY
tapes back on site and reuse them.

We do it constantly.