All the tapes without serial # need to have a Quick Erase Plus done on them and then the Tape Engine stopped and restarted. Then at that time the tapes will all have the correct serial #.
As for the current database, well I guess you can either delete the old tape entries or just initialize the database and let it start over. This type of thing can really mess up a database because the same tape can get two entries, one with the barcode serial # and one with the ARCserve generated serial #. From there it is just downhill with jobs getting mixed up between the valid and invalid entries.