The numbers on VG are according to the 31st. We don't know if that's the beginning of the day or the end of the day numbers so it's presumptuious to count the 31st. Either way, even if you do count the full of the 31st that still puts it at 3 days max, at least with VGC numbers.
VGC numbers in Japan go through the 1st. I'm also not sure where you got the idea that the numbers aren't through the end of that day. Pokemon X/Y came out on the 12th of October in the US. They showed up on the chart for the week ending the 12th.