Interrupted and incomplete backups can override legitmate ones

[DanielKinsman]

If an hourly backup is interrupted (e.g. shutdown/reboot), the latest hourly backup will be incomplete. When the next backup is made, the incomplete one will still be used, and may eventually become the latest daily, weekly or monthly backup.

If this happens quite frequently it is possible that there will not be a single complete backup kept. It also means that lincremental will use a lot more hard drive space than otherwise required, as hard links will not persist across backup sets.