1976-1977 serials ran D870001-D999999
i'd guess it was closer to first quarter of '76
iamtomstone..the semi autos are harder to date by serial than revolvers..
also anything after 1980 is harder to date as that's when smith changed their numbering system..
with that said..
in 1994 it lists a starting serial of VAMxxxx
in 1998 it lists a starting serial of VHN
certain prefixes were reserved..
thats all the info i have..maybe someone with better smith-fu
can add or clarify..