There may be old backup tapes with data that has not been over-written yet that you want to restore from.
If you have old tapes that have expired data on them, you can scan them back in and restore from them.
You may want to consider using the physical 'Read Only' toggle on the tape to protect them from being over written when you put them back in the library.
You should also go to the NV Configurator - Media Management tab and look at the setting for "Minimum life for imported backups." That number will determine what the new backup life, or expiration date will be on the data that you scan in from those tapes.