I get a few different boards in daily archive mode, and I have noticed something going recently that tends to make the digests longer: I often see messages repeat in the digests from day to day. Usually, I only see them twice on consecutive days, but I think there have been a few that I read three times. And I don't think I get every message twice.
Very strange. Or is it? I don't know why "daily" archives would contain messages from multiple days.