The early years were when REM shotguns were produced by craftsmen, not by push button operators.
The 870 was introduced in
1950 with 15 different versions of it in 12, 16 and 20 gauges.
Here's a little tidbit you can use to determine barrel manufacture dates without referencing the serial number. If the barrel hasn't been swapped since the gun was made, you can determine the year it was manufactured by the barrel codes.
If the barrel was swapped, at least you'll know when the barrel was made.
Remingtons manufactured after 1921 have a code located on the left side of the barrel near the frame that identifies the year and month of manufacture.
1. Codes started in 1921 using M
2. A 22 letter alphabet was used until 1975, excluded I. O, Q, V
3. When M came around again in 1943 they started using double letters MM
4. When they got to ZZ in 1953 they went back to single letters, A = 1954
5. In 1975 at Z they decided to start using the missing letters I, O, Q, V
6. 1976-1979 are I, O, Q, V
7. 1980 starts with a full alphabet in order.
9. After Aug 1999 they only stamp the date code on the box
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 Codes: [second (and third*) letters]
1950_______ WW
1951_______ XX
1952_______ YY
1953_______ ZZ
1954_______ A
1955_______ B
1956_______ C
1957_______ D
1958_______ E
1959_______ F
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_______ V*
2002_______ W
2003_______ X
2004_______ Y
2005_______ Z
2006_______ A
2007_______ B
2008_______ C
2009_______ D
2010_______ E
2011_______ F
2012_______ G
(*) On 8/9/1999, stopped stamping the barrels with the date code. They continued to mark the date code on the end flap of the shipping box.
They resumed stamping the date code on the barrel on 10/1/2001.