Mid-80's. Call S&W and they will tell you when it left the factory.
@1969
1977
No serial number given = no answer.
1969
1979
You must call S&W
80-81
You will have to call S&W
1986
You must call S&W
Call S&W with the serial number and they will tell you.
You will have to call S&W for the date.