I believe Xbox One will win November AND December NPD

[Arkaign]

I think you hit on a key that may severely harm them : "Microsoft should have really shipped more".

You can't ship what retailers don't accept or order. A lot of planning has to go into things, and retailers hate taking big risks. PS4 has been a solid hit all year long, while X1 has had fits and spurts. Worse, X1 has had SKUs that have been left to rot when newer more competitive ones are released (Kinectless did this to the $449/$499 Kinect bundles, and now AC/etc $349 bundles and $329 BF bundles are doing this to the vanilla SKU). So it's a lethal combo of overstock of bad SKUs along with not enough retailer demand in advance for the hot SKUs.

Sony seems to have produced MASS numbers of bundle SKUs for the BF to end of year period. And if something is in dramatically higher availability, it can heavily skew things.

Best case for X1 : somewhat narrow win for Nov, somewhat narrow loss for Dec, for an overall tie.
Worst case for X1 : somewhat narrow loss for Nov, moderate loss for Dec, for another ~150-250k in the hole overall.

I think the reality will be in the middle of that though.