Netbackup Catalog Backup

Originally our netbackup catalog backup job ran once a week writing to a store on our Storeonce appliance, keeping 6 weeks worth of backups.  At completion, we would receive an email indicating the DR and DR Package files.  A couple of months ago, we were requested by upper management to run the catalog backup job daily, and also to keep a copy on tape.  We changed the schedule, added the second copy to tape, and also changed the retention to 1 week on Storeonce and 6 weeks on tape.  When the job completes, we get the normal email with the DR and DR Package files as before.  But immediately following the catalog backup job, the image cleanup runs, and then we receive 2 more emails listing the DR and DR Package files from 1 week ago, like it's going back and modifying those files - maybe due to the 2 different retention periods we have - 1 to Storeonce and 1 to tape?  Just looking for some clarification as to what exactly Netbackup is doing.  We are receiving no errors of any kind and everything seems to be processing fine.