These Date Codes are also present on the Model 94 frames and barrels, and I am sure on many others.The marks on the inside of the frame, where the lower barrel seats when closed, are what I would call assembly stampings, and match frame to barrel, found on underside of shot barrel near forend lug, and also sometimes found on the butt stock under the butt plate.
Stevens 22-410: (Pre WWII has wood stocks, later years had tenite) Savage 24: (Joined barrels the entire length; top of tang barrel release lever; right side button barrel selector on Model 24, 24A, 24B; 24E was the first with barrel selector on the hammer often referred to as the 24E conversion when found on the other models that had button selectors) Savage 24 De-Luxe models: Joined barrels the entire length; top of tang barrel release lever; 24-DL & 24B-DL had right side button barrel selectors, 24C-DL started with a left side button barrel selector and later had the hammer barrel selector;24D-DL, 24E-DL, 24H-DL & 24J-DL had hammer barrel selector; all models came with satin chrome finish receivers and gold triggers and the 24J-DL also had a black painted receiver variant with no gold trigger.
Savage 24S: (In this case the S stood for side lever barrel release) Joined barrels the entire length; lack of center tang in the rear of receiver.
Models include 24S, 24S-A, 24S-B(not sure at this point it exists but follows logically in sequence so I include it) 24S-C, 24S-D & 24S-E.
"Collectors will find a date code stamped on every double-barrel shotgun in the Stevens brands produced between March 1949 and December 1968.
Usually, it is behind the hinge pin or ahead of the trigger guard on the bottom of the frame.
It will appear as a small circle containing a number and a letter.
The letters correspond to the years shown in the following table.
Significance of the numbers is not known."* *From page 1101 of Ned Schwing's 2004 Standard Catalog of Firearms, 14th Edition, published by Krause Publications of Iola, WI.
I would like to add that I have found this circle, or oval, containing one or two numbers plus a single letter, just about anywhere and everywhere on the frame, but only on the outside of the frame, never inside.
I have also found the circle or oval with letters and numbers on the barrel clusters, on the shot barrel or on the barrel assembly lug block.
While the letter within the circle always match on factory matching barrel and frame, the numbers never match, or at least that has always been my experience.