Hi guys. This is my first post so go easy on me. 
Recently, I've been trying to chart a comparison of the last few console generations (just Sony and MS) and I'm wondering, where do these numbers come from? How do you have data back to 95?
So far, I have figures for the current gen (PS4/X1) and the last gen (PS3/360) but I can't find much beyond that. I can find overall totals and some scattered information but not in the detail of the more recent generations.
For the record, my eighth gen data comes from the VGChartz hardware comparison tool, and my seventh gen data comes from the NPD data in the table on this page (scroll down for it - it's under "NPD sales figures monthly table")...
http://vgsales.wikia.com/wiki/NPD_Seventh_generation
As I go back further than that, though, the data becomes more generalized. I'm charting the seventh and eighth gens by monthly sales but I can only find yearly totals for the sixth gen, and almost nothing before that.
Does anyone know where I can find sales figures for the PS1, PS2, and original Xbox? Preferably monthly sales figures if they are actually published anywhere. I tried looking for more info at some of the sources cited on that wiki but, unfortunately, many of them are just dead links now.
Thanks in advance guys. Nice place you have here. 