http://www.joystiq.com/2012/05/24/npd-monthly-reports-integrate-walmart-data-starting-next-month/
Despite being revealed this past February, the past several months of NPD reports haven't included Walmart's numbers.
"Our enhanced retail coverage, including the addition of several new retailers, begins with May data released on Thursday, June 14," Riley told me in an email yesterday. While he couldn't supply a list of all of the retailers involved, he told me, "Yes, it does include Walmart."