Do I understand that if a file is in the catalog but missing from the backup set it will never be replaced?
For example, I swap out backup disks. I have two backup disks. One is in a bank and the other attached to the machine making backups. When I swap the disks, all files added since the last time it was in the system are missing from it's copy of the backup. If I understand what you're saying, none of these files will ever get backed up, because the catalog is happy. Is that right?
There's a law of nature that if there are two independent lists which are supposed to be of the same, they will, over time, drift apart. This is sometimes referred to Murphey's law. Unforeseen things will happen that cause the two presumably identical sets of data to be different. Why have the "catalog?" Why not simply compare the system with the backup and make them alike? Then these problems created by a independent list of files could not happen.
Do you have a "Regenerate Catalog" function that inventories the Backup and creates a new, accurate catalog? If not, it's unclear how one would ever make the catalog accurately reflect the contents of the backup. When I swap out my drives, missing files will be in the catalog but not in the backup and if I were to delete the catalog and redo the backup there will be files in the backup that were deleted, but the catalog has no way to know that, so they will remain in the backup forever.
Perhaps I have misunderstood your method. If so, please help me understand.