The source of the sales data matters. Hardware sales reported by Nintendo from their own records (for financial reports to investors and PR out of the blue and stuff) is shipments. Even if they use the word "sold." PR accompanying NPD results use sold-through numbers provided by NPD.
906k hardware sales in March were from NPD (US only). 925k Zelda sales in March were a combination of NPD's sold-through number and Nintendo's digital sales. Nintendo didn't reveal their internal figures until their annual report a couple weeks later. The number they gave at that time was 2.76 million. Those are global shipments (including digital sales).
How would Nintendo know sell-through numbers? Do you think retail chains share that info with Nintendo? If they did, why would Nintendo pay for NPD numbers? All Nintendo knows is what it sells to retail stores: shipments.
