I found this at a different forum so I can't be sure it is correct.
Modern Remington barrels are stamped with a Date/Code, which denotes when it was made.
Remington Year of Manufacture Codes maybe found on the barrel of your Remington shotgun, on the left side, just forward of the receiver.
The first letter of the Code is the month of manufacture, followed by one or two letters which are the year of manufacture.
For shotguns with removeable barrels, the code will be valid for the manufacture of the barrel; maybe for the receiver, as barrels do get switched around.
Month Codes: [first letter]
B - L - A - C - K - P - O - W - D - E - R - X
1 - 2 - 3 - 4 - 5 - 6 - 7 - 8 - 9 - 10 - 11 - 12
Year:______Code: [second (and third*) letters]
1960_______ G
1961_______ H
1962_______ J
1963_______ K
1964_______ L
1965_______ M
1966_______ N
1967_______ P
1968_______ R
1969_______ S
1970_______ T
1971_______ U
1972_______ W
1973_______ X
1974_______ Y
1975_______ Z
1976_______ I
1977_______ O
1978_______ Q
1979_______ V
1980_______ A
1981_______ B
1982_______ C
1983_______ D
1984_______ E
1985_______ F
1986_______ G
1987_______ H
1988_______ I
1989_______ J
1990_______ K
1991_______ L
1992_______ M
1993_______ N
1994_______ O
1995_______ P
1996_______ Q
1997_______ R
1998_______ S
1999_______ T
2000_______ U
2001_______ W
2002_______ X
As maybe seen, the year code letters duplicate; some knowledge of when the model was introduced should resolve the actual year of manufacture.
SO, if (for instance) your Remington 1100 LT-20 has a Date Code of, say, "AZ" - that would indicate a manufacturing date of March 1975 ("A"=3=March; "Z"=1975).