Come on, it's clear that VGC overtracked Forza 3. NPD numbers for october are 175.000, and in november Forza 3 wasn't even in the top 20. That means that november sales for Forza 3 are probably below 250.000, considering that number 10 sold 315.000 units.
So, according to NPD numbers Forza 3 sold a MAXIMUM of 425.000 units in october/november in the US. And it's probably even less than that. That means, what, 475.000 units sold in North America? But like i said, probably less than that. But according to VGC the game sold 610.000 units in the same period. So that's 28% more than NPD numbers, and maybe even 30-35% more.
Anyway, the Turn 10 statement actually confirms that VGC overtracked the game. According to them the game just reached the milestone of 2 million units sold, probably sold to consumer, which bye the way is a very good accomplishment. The VGC number for Forza 3 is currently at 2.39, so yeah, it is overtracked. By how much? I don't know, probably around 300.000, maybe a bit less. Does it matter? Not really. UNLESS they don't change their numbers of course.