Norton Ghost 15.0

I'm trying to determine whether my backups are working properly.  Under the Norton Backups folder I see several fbtFiles.  The modified dates on these files do not change whenever I run a new backup.  There is new data to be backed up so I'm wondering what these files are for.  I see other files with .iv2i extensions that are created when a new backup is run.  I'd like to know what the ftbFiles are.