For those of you interested in the details, here is how %reclaimable is
calculated, where:
maxocc is the maximum occupancy of the tape.
occ is the actual occupancy of the tape (expired files not counted).
estcap is the estimated capacity

For full onsite volumes:
  100 * (maxocc - occ) / maxocc
For filling onsite volumes:
  100 * (maxocc - occ ) / (estcap or maxocc, whichever is greater)

So yes, filling volumes can be reclaimed, but the space from the
end of file mark to the end of the tape isn't considered at reclaimable
space in the formula.

For full offsite volumes:
  100 * (maxocc - occ) / maxocc
For filling offsite volumes:
  100 * ((estcap or maxocc, whichever is greater) - occ) /
            (estcap or maxocc, whichever is greater)

The important difference here between offsite and onsite filling volumes
is that the space from the end of file mark to the end of the tape IS
considered reclaimable for offsite filling volumes.  It is considered
reclaimable because the tape is taken offsite and is essentially like a
full volume now because it won't be written to again.

Dave Crockett - ADSM development