As Technical suggests, and this seems to have been the experience of others here, you're probably better off selecting "local drives" rather than "folders", since it sounds like you're doing the whole drive anyway.
Maybe the team can figure out -- or already know, and can explain in relatively simple terms -- why the status info seems to update fine if you scan using local drives rather than using folders and including all folders.
(Edit) As a P.S., for the purpose of keeping stats updated I don't think it matters whether or not you include archives in the scan. I always do anyway, but there have been times in the past when I didn't bother and I'm pretty sure the last-scan info still updated ok.