I'm not disagreeing with your numbers, but I am wondering if Microsoft put such a big focus on NA sales back when 360 launched, as they did now? If 360 sales were "low" within the first 3 months might be more supply limited because they might have had a higher allocation in the rest of the world? How do the numbers match up then?
Yes 360 was VERY supply constrained. So was PS3 it's first 2 months.
MS/Sony just weren't able to manufacture many PS3/360 at launch. They were able to manufactore a ton of One/PS4.
The 360 was supplied constrained and was gaining momentum. This is a completely different scenario from the XB1 which had plenty of supply and no momentum.
360's first post holiday 6 months:
January 2006 -249k
February 2006 -161k
March 2006 -192k
April 2006 -295k
May 2006 -221k
June 2006 -277k
Solid sales but nothing explosive nor indicating a huge surge when not supply constrained. I dont recall for 100% sure but I am 99.9% sure 360 wasn't in shortage by Feb/March, it just experienced somewhat weak sales those months.