VGchartz isn't reliable. They're just estimating and literally "guess" and sometimes "update" their numbers after official numbers show up.
here's an example:
The Last of Us (PlayStation 3) - Sales, Wiki, Cheats, Walkthrough, Release Date, Gameplay, ROM on VGChartz
They have that as only selling 5.3M yet the official numbers from Sony has said TLOU sold over 7 million on PS3 alone:
The Last of Us Remastered Sales Cross 1 Million Worldwide
They got halo as 12 million while Official M$ numbers are 14 million.
Basically, don't use them as official numbers.
I don't think they account for digital and other factors like free from various services, bundles, etc

@ VGCHARTZ

I see you have nothing to logical to rebut with. Dueces