Seece, seems like you're grasping at straws here. The article clearly states 2.3 million consoles sold, no amount of calculations from your part will get that number up to 2.6 million.
There is however one thing that could explain the difference with Vgchartz. Charttrack tracks about 90% of the market. (at least they used to, don't know if that number still holds up) That 2.3 million might be the raw number they tracked. Extrapolating for the whole market would increase the number by about 10% and get it over 2.5 million. If that's the case the difference is solved.