You can use --force flag when backing up. It will “force re-reading the target files/directories”, as it says in the manual. It is not the same as a new full backup but you can use it. You could also restore the latest snapshot from time to time and compare files with the source files. It is not ideal but it can give you that peace of mind that you could be looking for. check --read-data --read-data-subset also gives you another way to verify backup integrity as mentioned here by @fd0.