I bought a M1 Carbine years ago through the NRA (around 1963-65). It is in great shape but the serial number has me confused. It was manufactured by Rock-Ola and the serial number is 1906595. This number doesn't fit the serial number list I found online. They show:
1662520 - 1762519 Nov. 1942 to Nov. <phone> - 4632099 Nov. 1943 to March 1944
It does have an adjustable rear sight so the carbine was probably rebuilt by the government following WWII.