How does TM know if it can reuse file from the previous backup or should create a new version. If it's just timestamp then it's not such a good idea, it should use hash of the content, and if it has and stores content hash it can and should verify backups once in a while to e sure against bad sectors etc. Doesnt have to be on each backup, and doesn't have to be all files at once, but it can, say, check backed up file content once a month/week or so.