My 12ga has "439" between the barrels, and a "U" on the left barrel face under the extractor.

One 16ga has "941" between barrels, an "S" on right barrel face.
Other 16ga has "631" between barrels, an "N" on right barrel face. According to Cody letters, the first gun started inspection in June 1939, finished in Jan 1940, and was made for a named individual. The second started and finished in July 1940, was made for A&F.