I found this searching for the date of my 36 not sure if it is spot on
"Early J frame serial numbers
For models 36, 37, 38, 49, 50 and pre model number versions.
1950 = start at 1
1952 = 7369 - 21342
1953 = 28916
1955 = 55050 - 75000
1957 = 117770 - 125000
1962 = starts at 295000
1969 = ends...