Keep in mind, with regard to the scan date, that that only gets updated when you've run a "local drives" scan. If you scan using "folders", the scan-date doesn't get updated even if you've selected the whole C (or whichever) drive.
Maybe that's something the Alwil team could look into for future versions, getting avast to treat a "folders" scan for the entire drive the same as a "local drives" scan.
Best,
Mike