Yes, I understand that Underwood was one of the manufacturers of the USGI M1 Carbines, and then their was the commercial producers of the rifles for the masses as well.
It's kinda my thing ya know........Guns and all.
Having said that, the factors I mentioned will dictate the value of the carbine, as collectors are a finicky bunch with regards to originality of the rifles they buy. Underwood is one of 11 manufacturers, and the third most common, so they are not too rare of a maker to find, behind Inland and Winchester. CMP paperwork would help increase the value as a letter of provenance, avoiding the possibility that the rifle was/is an import rifle.