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?
Harrington & Richardson used the Prefix AT in 1983.
How old is my Topper 88 HARRINGTON AND RICHARDSON GUN serial number
Serial numbers were not required before 1968
"AY" serial prefix = 1982.
Harrington and Richardson used serial numbers that started with AM in 1974. The company had similar shotguns being built from 1974 to 1981.
"P" prefix indicates 1953
1971
1980
50-250 usd
Az476987
No way to answer without the serial number.
No public records- sorry