I think my Underwood has a NPM stock, but they were often swapped around, especially after the war. The matching serial number on the stock was a common Israeli addition, so it was probably applied after the stock was swapped.

How does yours shoot? Mine, as I said, is the tightest shooting carbine I have ever owned. Of course, I generally only own one M1icon Carbine at a time, though I try to always have one continuously for over 27 years, now.