Of course Sony/Nintendo/MSFT can use NPD and other estimators to figure out how many consumers brought their product from stores, but I don't think people are debating that (at least I don't think). These sort of press releases of official #s from the manufacturer are based on exact, factual shipments from their factory to the stores. You can't fake or fudge those numbers because it's illegal and the SEC and investors would have a field day. If they knew exactly what stores sell to consumers, then there would be no need for NPD, and they would release their own NPD reports every month.
The manufacturer knows exactly how many units they produced though, and how many they shipped/sold to the store (these press release #s). The manufacturer (Sony/Nintendo/MSFT) report these #s and revenue to investors. The stores then take the product they bought, mark it up to the MSRP, and sell it so they make a profit on it. NPD & others measure these numbers.
Stores do not call up Sony/Nintendo/MSFT corporate every day and say "OMG, we sold 3 more units, yay!" However, they do say, "we need another shipment of 100 units for next week." The manufacturer then packages these up and ships them out to the retailer, and marking it as a sale (because it was sold to the retailer).
The fact is, that all consumer products/electronics companies count the products they ship out of their manufacturing facility as a sale, even Sony/Nintendo/MSFT.
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