SAVAGE STEVENS 350A 410 SXS - MFG DATE

I just purchased the above and am trying to establish it mfg date. It has an "O", "A", and and A in circle and a J in a circle on the frame in front of the firing pins, and on the barrel and fore stock. It also has an 14 B in a circle on the bottom of the frame, just behind where the fore stock attaches. From what I can find out, it looks like the 14B indicates it's a 1950. If that is correct, what are all the other marking? Proof marks, etc? Also, what is the choke? Both sides measure about .391-.393, which I believe would be FULL & FULL. Can post photos if needed.