I hope this helps all Marlin owners:

The modern Marlin 1895 was introduced in 1972 and that year they had a B0 (bee zero) serial number prefix. Subsequently, the first two numbers of the serial number designates the year of manufacture. Up to 2000 subtract the first two digits from 2000 to get the year of manufacture and after 2000 subtract the first two digits from 2100 to get.

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1. Firearm serial numbers were date coded by a prefix within the s/n, as signified below. For example a Marlin model 39A with a serial number of N1255X would have been made in 1955 while a 1894 in 44 magnum with a serial number of 2510509X, would have equated to 1975.
2. The serial number, depending on the model of rifle, will either be located on the upper or lower stock tang, bottom of the receiver, or side of the receiver. Below are the manufacturing date codes, which are the first one or two characters of the serial number. Please note this list is NOT INCLUSIVE of all Marlin firearms.
3. Marlin factory records (Regular factory letter fee) Lever action Marlin models with factory records: 1881 1889 1893 1895 1888 1892 1894 1897 All lever action models are found in one serial number range from 4096 to 355419 A small number of earlier serial numbers are available including: 286, 673, 1069, 1542, 1774, 1893, 1912, 2020, 2453, 2475.
4. Model 39s with a 'star' stamped on tang, were considered high grade guns by factory inspector and will command a premium in better condition examples. NOTE: Model 39s made prior to 1932 that have no prefix or prefix S on serial number, should not be used with high-speed ammunition.

Marlin Year of Manufacture
Marlin year of manufacture maybe determined from the following list of letter/numeral prefixs to the serial number; this coding only applies to serialized rifles:
1946-C
1947-D
1948-E
1949-F
1950-G
1951-H
1952-J
1953-K
1954-L
1955-M
1956-N
1957-P
1958-R
1959-S
1960 (August)-1961-U
1961 (August)-1962-V
1963-W

Marlin 39a Serial Number Date Of Manufacture

1964-Y,-Z
1965-AA
1966-AB
1967-AC
1968-AD, -68
1969-69
1970-70
1971-71
1972-72
Starting in 1973, the year of manufacture maybe determined by subtracting the first two digits of the serial number from 100:
Example: SN 2512345 would have been made in 1975 [100 - 25 = 75] and SN 94365295 would have been made in 2006 [ 100 - 94 = 06 (2006) ].
For Marlin Rimfire Rifles [non-serialized]:
From 1962 thru 1968 Marlins rimfire rifles (other than the 39 series lever actions) used a two letter date code that was stamped on the barrel. This date code is different than the one already listed, as Marlin rimfire rifles (other than the model 39 series) did not have a serial numbers until required to by Law after 1968. The first letter of the date code represented the month of manufacture while the second letter indicated the year. This date code was usually stamped on the left side of the barrel just in front of the receiver. The first letter of the date code is as follows:
A = Jan.

Marlin 336 Dates Of Manufacture

B = Feb.
C = Mar.
D = Apr.
E = May
F = June
G = July
H = Aug.
I = Sep.
J = Oct.
K = Nov.
L = Dec.
The second letter of the date code is as follows:
F = 1962
G = 1963
H = 1964
I = 1965
J = 1966
K = 1967
L = 1968
So a date code of 'JK' would indicate that rifle was made in October of 1967.This question comes up from time to time and I'm sure the information has been already posted but could not locate it with a quick search. Was easier to cut and paste this list from my own file and as far as I know it should be correct. If I made a mistake I'm sure that someone more knowledgeable will let you know of any corrections that need to be made.
Marlin's year of manufacture for the 39A is determined from the following list of letter/numeral prefixs to the serial number:
1939 - no letter prefix

Marlin 336 Serial Dates

1940-1941 - B
1945 - C
1946 - c (lower case)
1947 - D
1948 - E
1949 - F
1950 - G
1951 - H
1952 - J
1953 - K
1954 - L
1955 - M
1956 - N
1957 early - P
1957l ate-1958 early - R
1958 early - 1959 - S
1960 early - T

Marlin 336 Serial Number Date Of Manufacture

1960 (August) - 1961 - U
1961 (August) - 1962 - V
1963 - W
1964 - Y & Z
1965 - AA
1966 - AB
1967 - AC
1968 - AD or 68
1969 - 69
1970 - 70
1971 - 71
1972 - 72
Starting in 1973, the year of manufacture maybe determined by subtracting the first two digits of the serial number from 100:
Example: SN 2512345 would have been made in 1975 [100 - 25 = 75].
Hope this helps

Marlin 1893 Rifle Serial Numbers

Tom