Yes, it usually means the recoil lug is setting back in the stock.
Did it come cracked ?
I believe so.
do the cracks spread on these with time. surprised to hear of it on unissued ones.
You need a bit of clearance between the upper tang and the inletting for it in the stock-otherwise it will act as a recoil lug and crack the stock. You see this in M1903 Springfields as well. The fix is to add a shim (brass shimstock or a slice of aluminum pop/beercan) between the rear face of the recoil lug and the bearing surface for it in the stock.