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
"P" prefix indicates 1953
Harrington and Richardson used serial numbers that started with AM in 1974. The company had similar shotguns being built from 1974 to 1981.
"AY" serial prefix = 1982.
1980
1971
No public records- sorry
50-250 usd
Az476987
No way to answer without the serial number.