Harrington & Richardson used the Prefix AT in 1983.
S prefix is 1956.
1871
1980
1987
1971
Harrington and Richardson used serial numbers that started with AM in 1974. The company had similar shotguns being built from 1974 to 1981.
40's and 50's
the topper model 88 is a 1985 model according to the blue book of gun values
The H&R model 925 second model was made from 1964-1972,The third model was made from 1973-1978.The first model 925 defender was produced from 1946-1947.You did not state which model defender you have?
I THINK your H&R 922 was made in 1948. In 1942 they added a letter prefix. changing to double letters in 1961.
Made by Harrington & Richardson as their Model 120, it began production in 1941. In 1942, they stopped production of civilian firearms due to WW 2. Only made for 2 years.