“Area 51″ Model 60? a.k.a “It officially does not exist”?

Had a customer call me about his model 60, when discussing the serial number, he said he got it from a tag (a tag?) on the grain tank side of the combine. Started with  a “S” (if I remember correctly) and a number that makes it made between 91162 and 95389.  Problem is there is no record of any combine being made in that range as it was a “gap”.  But this was during the WWII years, so perhaps this one was cobbled together and never stamped with the serial as it officially was not to exist?…. I have asked the owner to look for that stamp on the other side…