I think would have to be items that folks aren't tracking. I can tell you how much some items have been from the start. I assume folks track different things for different reasons. So, yes(?) at least on the items I track I would know. Edit to add - I agree with you that "sales" isn't always what they appear to be. In this game and only speaking about this marketplace, would be easier to tell since different play styles etc watch for different items to be on sale.