Pap, you have it all wrong. NPD tracks more than games, but they track all the games that hit retail shelves.
NPD sells this information to their clients, made of sales analyst & other such companies that want to pay X amount of $ for the info.
NPD also Officially releases TOP 10's exclusively to NeoGAF every month as a courtesy for not posting the entire leaked NPD confidential report to the internet. -NPD was trying to plug its leaks, no need to pay for the info if you can find it for free on the internet-
Just because the whole NPD doesn't get posted on NeoGAF anymore doesn't mean that who ever was leaking it doesn't still have access to it.
IOI or whoever is running VGChartz now, probably knows one of the dozens or hundreds of people out there that have access to this info and are still willing to share it.
The numbers from VGChartz that needs to be tracked & posted are the ones that come out weeks & days before the official numbers.
They have constantly posted "up-to-date" numbers during a tracking period only to "adjust" those numbers after the official count came out.
If you check their numbers for past weeks all the way up to current, I have no doubt that what you will be looking at will be as accurate as any other tracking service, but those are not what is being questioned.
& for the record, being 100k off is not very close. (unless we were speaking in the millions)
If I were selling you a house, & you absolutely loved it, asked how much it would cost, & i repled with "$500k"
then when it was time to sign the paperwork and now the house really cost $600k, I can guarantee that you are not gonna reply back with
"That comes close to what you said".
But either way, that's enough about VGChartz. I'm anticipating GP's results from her observations as I haven't even looked at VGChartz in atleast 2 years.
edit: slightly beaten