IIRC, the Model 336A was first introduced in 1948.
All Model 336 serial numbers have a yearly prefix code, either alphabetic or numeric.
These serial codes also work for the Model 39a, as well.
Early serial numbers located on the lower tang under the lever; Later ones on upper tang.
C-1946
D-1947
E-1948
F-1949
G-1950
H-1951
J-1952
K-1953
L-1954
M-1955
N-1956
P-1957
R-1958
S-1959
T-1960
U-1961
V-1962
W-1963
Y-1964
Z-1964
AA-1965
AB-1966
AC-1967
AD-early 1968
68-late 1968
69-1969
70-1970
71-1971
72-1972
27-1973
26-1974
25-1975
24-1976
23-1977
22-1978
21-1979
20=1980
19-1981
18-1982
17-1983
16-1984
15-1985
14-1986
13-1987
12-1988
11-1989
10-1990
09-1991
08-1992
07-1993
06-1994
05-1995
04-1996
03-1997
02-1998
01-1999
00-2000
99-2001
98-2002
97-2003
96-2004
95-2005
94-2006