Wow, that's a head-scratcher!

The 'machine cuts' in the wood, for the action, barrel, and lightening-channels, all look correct to me. (I am directly comparing them to two original stocks).
The 'head of the hinge-bar' area appears to have has been 'whittled on' a bit.

The wood does not appear to be black walnut. It could be Italian walnut.

The "circled P" proof looks pretty crisp and closer to the rear of the trigger-guard than on my stocks.
(Are there any tiny inspector initials or numbers, right behind the trigger-guard)?

I'm stumped. The inside looks good.

The oversize butt-area is very suspect??? An uncompleted and discarded stock would not be likely to have a circle proof?

(I guess we need to see pictures of the butt-plate area holes).

FWIW - In my 'junk box', I have a couple of Krag butt-plates that were reduced in size on 'sportered Krags'. That is not all that obvious, until I compare them with a normal size one. (I'm grasping at straws, here).

I don't know.  I see a yellowish hue to the stock.  Is it Italian walnut maybe?

Mystery deepens .... the butt-trap looks correct and it is grooved to store the oil bottle, too.

Speculation… how bout this was at sometime a stock for a '73 carbine that was left from earlier inventory?  And, during the period of the shortages for Krag replacement carbine stocks (1901-2) was 'altered' to see how much work would be needed to adapt it to the Krag.   That would account for the double holes and for the 'fat' size.  That might also even account for the "P".  If this (or prototypical work for the '03 adapted to the Krag) was involved, the decision as to cost and timing was probably found to be prohibitive. 

I'm gonna feel pretty silly if I overlooked a wood shim like that 

I'll take a close look when I get home this afternoon.

Rcat - Your butt-plate may be bent in the tang or other areas, due to efforts to make it fit ... 'more better'.

If possible, try a different plate after you've checked for 'wood obstruction'.

Good observation detective Chuck concerning the butt plate not seating properly!

I purchased, sometime ago, a beat-up 1896 carbine that had a cut down rifle barrel and lyman peep sight.  The carbine was also missing the rear sight and hand guard.

I wanted to play around with it and had the parts to restore it to a proper 1896 but...I quickly discovered that original barrel bands would not fit due to the width of the barrel.

The workaround that a previous  owner used was to install a 1903 or mauser barrel band (fairly common).

I also noticed that the width of the barrel apparently has caused the nose of the stock to crack by forcing outward pressure on the barrel channel (see picture).

Regardless, you have a very nice carbine and I hope your able to resolve all your issues with it and "Get to chooting that thing!"