| Ninjahound101 said: "NPD covers roughly 60-65% of the U.S. retailers.[7][8][9] It notably does not cover Toys R Us (since Oct 2007) and Sam's Club retailers, but it has covered Amazon since Nov 2007 and Walmart since Feb 2012.[10][11] Although, NPD does not track Toys R Us, they do estimate Toys R Us and other retailers' sales using various algorithms and estimations. In February 2008, the firm announced they will begin tracking online game subscriptions for PC sales data and Xbox Live online subscribers on a quarterly basis and then start gathering data from digital distribution later in 2008." http://vgsales.wikia.com/wiki/NPD_Group Pachter says that NPD is 85-90% accurate so 70% seems about right 800K is close to 1 million |
You're right that NPD isn't totally accurate but it's the best estimate there is and is used by Nintendo themselves.
Also retail sales of 3D World would have been lower as Nintendo added digital in that ~220k number.
