This was some good information that I found from Gun Digest :
1. Stevens used plain numbers from their first double in 1878 until 1913.
2. Letter prefixes crept in on the serial numbers used on both hammer and hammerless doubles from 1913 to 1939. They always signified a change in mechanical design or manufacturing process which resulted in an interesting variant.
3. From 1940 to 1948 no serial numbers were used on doubles, only capital letters, usually in groups of three or four, the letter(s) sometimes enclosed in a circle, along with an inspector’s symbol ( a heart , a diamond, a spade or some such ‘shape’, on the bottom of the frame behind the hinge pin.
4. From 1948 to 1968 the letter symbols under the frame were changed to a ‘Capital letter with a one or two digit number’ in a 1/4″ circle. This was a date code which you will find illustrated in the Savage-Stevens-Fox pages of your Standard Catalog of Firearms.
5. From October 1968 to March 1988 Savage/Stevens/Fox B doubles are serial numbered in a completely new serial number range beginning at A000001. The six digit (always) numbers, stamped only on the left side of the frame, not on the barrels or fore end or on the wood, are preceded by capital letters from A to E. The letters do not correlate to production years. The letter prefix accompanied the Savage/Stevens/FoxB/Springfield serial number on every gun they made from 1968 on. Beginning about 1978 numbers 1 to 20 were also stamped on the three major components, frame,barrels and fore end iron, to enable the factory to keep 20 guns of like model together in a group for packing in the standard 20 gun shipping carton.
