Hey Tommy,
absolutely.! As Dimitar said the new version counts unique objects present in the IDB. Most likely new unique objects have been created within the last four years. The original objects (with former FQDN, drive letter) are still protected on media vaulted (located in safe). Let's say you had 20 TB data backed up on an old file server that was replaced with a new file server within the last four years Data Protector will count 40 TB today since both unique objects exist in IDB. A single protected session is enough.
The only way to get rid of the additional capacity is to purge unique objects from IDB. Before you go ahead and throw away precious catalog data I would recommend to save it into MCF and store them with the data. This allows you to restore catalog quickly in case you need them. Not sure if removing catalog protection is enough. From my understanding objects with an active data protection are counted since objects without active catalog protection are still valid for restore.
Regards,
Sebastian Koehler