Today the data.version is a global state that is recorded in the upgrade directory. If a user upgades their DJ and then subsequently restores a backup from a date prior to the upgrade then the upgrade tool will not detect that the restored backend needs to be upgraded.
This issue can be closed when it is possible to upgrade a restored backend. It implies:
- storing a per-backend data.version
- including the data.version in the backup
- upgrade tool should upgrade each backend.