I believe they say sold because they just simply don't know if it's blocked or sold. Sometimes when I talk to the regular line, they'll tell me I'm going to be transferred to the Platinum line since they have more power and see if the seats are really available or not. Then there are seats under permanent airport control that they can put in a request and a day or two before my flight I'll get a text telling me my seat is confirmed. In fact I don't think I've ever not gotten the seats I wanted.