Bob sorry didn't quite read your answer 100%, maybe I wasn't clear asking,.
So to confirm if the directive tells the backup to run a Differental Incremental of ALL_LOCAL_DRIVES
The drive files backed up will be a differental incremental but the SYSTEM STATE will alway be a full back regardless of of Full, differentail incremental etc.
In priciple I will only need one restore and no roll-up restores.