A very subjective estimate based on my limited experience suggests that 1 tape in 5 will survive for only 20 uses. The ages of the tapes are uncertain, but the tape drive is still less than 1 year since purchase. This estimate strikes me as low, but even if off by a factor of three or four should not double the cost of tape retirement. A more precise estimate of tape requirements will require a complete inventory of disk space and determination of what fraction needs to be backed up. This is currently being done as part of a more general inventory of departmental hardware and software, but will not be completed for some time.
Backups are too important to wait for completion.
Synopsis Backup status for various departmental disks.