I mean, there are often huge differences between them and other sources like Famitsu.  Also, many people complain about the "Others" data, and claim it is totally made up.  Quite frankly, I don't even trust professional companies like NPD or Famitsu.  Even them seem to do a lot of mistakes and using rough estimations instead of confirmed numbers.

 I am even questioning the numbers of past consoles.  If you look on Wikipedia, you will see that each console  has a number sold.  For example, Sega Genesis supposedly sold 29 millions, while Super Nes supposedly sold 49 millions.  This is just an example.  I don't even trust those numbers.  Who made them up, and based on what?  They could have been totally made up and taken as facts.

 It seems that these numbers were never terribly accurate, and will never be.

Do you trust your government? Who is there to trust and who not?

I think you should check this thread:

http://vgchartz.com/forum/thread.php?id=13607