I think they track results of foreclosure auctions, record anything that goes back to lender as a REO, then remove them as they become aware of sales. They are good at tracking foreclosures (a house can be recorded on the day of the auction) but they are not quite as good at learning about sales (for example, one of 7 REOs they see in 4S has actually been sold on 6/11, they just don’t know that yet).