And I just got one with omega date code. That extends the 6AM into 1940!
From the ebauche AV 120.
1939 w/ shield symbol in 1939 case. See http://www.mybulova.com/node/4393
Jerin's unknown w/ 1938 cresent moon date code. See http://www.mybulova.com/watches/1938-unknown-2993?page=1
The one I have has the square date code=1946, I guess.
square date code for 1936?
Arrow date code