Diomedes -
Time will tell exactly how many X360s have sold. Nevertheless, we have 100% accurate US, Canadian and Japanese Charts, with alot more accuracy in Europe thanks to Italy, UK and a few other's being close.
I don't think they're off by much. You just hate the Xbox 360, and hope it fails, and try to use every possible excuse to criticize VGC data when it "doesn't go your way". You do that with MC-Famitsu when PS3 sales are lower.
The fact is, this site has never, ever adjusted it's figures for shipment data. If anything, the shipment data confirmed alot. I think the only time that VGC data had to re-balance data due to shipping was when the Wii launched, and Nintendo announced only 3.2m units had been shipped and sold as of the EOY.
Back from the dead, I'm afraid.
