Got more for you;
The lower tang number is generally conceded to be a serial number. It started at one digit then went to 5 digits. When they had to go to a 6th digit they started with an A prefix instead and ran it up to the A and 99999 then started over with a B prefix and did work their way up the alphabet. The tang # should also show up on the right side of the barrel at the frame, and on the stock on the right side where it meets the reciever, on the inside of the buttplate and on the right rear of the foream--unless those parts have been replaced
Finally, there are a bunch of other features such as type of adjustment (or lack of same) for fixing lever droop that can help identify age. Also is the extractor at the 6 O'clock position at the bottom of the barrel breachface, or at the earler 7O'clock position. A good reference is a single shot book by Tom DeHaas. I have one and will help you out Finally I suggest the ASSRA (American Single Shot Rifle Assoc.) web site and ask over there. They helped me out big time on a somewhat rare Stevens 418 Walnut Hill based on a Favorite action