I can say that the Smith and Wesson model 4566 has been made from 2000-to date.You could contact Smith and Wesson directly and they may identify the correct year of your pistols manufacture.
just bought a used 4566 for wifey. She loves it. Exc condition. paid $430 dollars U.S. SILVERBACK , OVER AND OUT.
email the serial# to smith & Wesson and they will respond with the date
K 7981 smith&wesson
1969
1880
1961
@ 1967
1948
The smith and Wesson model 6906 was made from 1988-1999.I am afraid that is the best I can do.You may want to contact smith and Wesson and see if they can be more accurate in terms of a production date.
1947
76-77
1962-69. If you want it narrowed down further, call Smith and Wesson.