I could be wrong on the year/month numbering for the 1942-1946 trucks. Below are the codes for the year and month. This came from U.S. Army Chevrolet Trucks in World War II 1 ½ ton 4x4 By Didier Andres. So its looks like your first truck (6MS12 37837) was built in Dec of 1941. The second truck (9MS40 23748) is a WPB truck built in April of 1945. I’m still learning about the Chevy and GMC civilian war time trucks
