Shimano code system:

Shimano Year

A
1976
2002
B
1977
2003
C
1978
2004
D
1979
2005
E
1980
2006
F
1981
2007
G
1982
2008
H
1983
2009
I
1984
2010
J
1985
2011
K
1986
2012
L
1987
2013
M
1988
2014
N
1989
 2015
O
1990
 2016
P
1991
Q
1992
R
1993
S
1994
T
1995
U
1996
V
1997
W
1998
X
1999
Y
2000
Z
2001

Shimano Month

A
January
B
Febuary
C
March
D
April
E
May
F
June
G
July
H
August
I
September
J
October
K
November
L
December

Mountain

XTR

M900 1992 8 Speed

M910 1995

M950 1996 8 Speed

M951 1998 8 Speed

M952 1999 9 Speed

M953 1999 9 Speed

M960 2003 9 Speed

M965

M970

M971

M972 (Shadow)

M980 2011? 10 Speed

M981

M985

M986

XT

M700 1983
M730 1987
M732 1989 6-Speed
M735 1990 7-speed
M737 1994 8-speed
M739 1996 8-speed
M750 1999 9-speed

751

M760 2004 9-speed

761

M770 2008 9-speed

771

772 (shadow)

773 (shadow)

M780 2011 10-speed

781

786

LX

M560 1993

M563 ’94

M565 ’95

M567 ’96

M570

M571

M580

M581

SLX

M662

• M663

M670 2012

M675

Road

Dura-Ace

7100 1973
7200 EX 1978
7300 AX 1980
7400 1984 6-Speed (1987 7-Speed) (1988 8 – Speed)
7600 1985 Track
7700 1996 9 – Speed
7800 2003 10 – Speed
7900 2008 10 – Speed (7970 ’09 Di2 10spd)
9000 2012 11 – Speed (9070 ’12 Di2 11spd) (7710 ’12 Track)

Ultegra (600)

6000 1974
6100 1976
6200 1978
6300 1981
6400 1988
6500 1997 9 – Speed
6600 2005 10 – Speed
6700 2009 10 – Speed (6770 ’11 Di2 10 – Speed)

105

5500

5501

5600

5700 2011 10 – Speed

5701


Shimano PDF Catalogs:

1978 (6.7 MBs)

1982 (7.8 MBs)

1987 (8.3 MBs)

1989 (7.8 MBs)

German

1991 (19.2 MBs)

Dealer

1991 (4.1 MBs)

German

1992 (3.2 MBs)

German

1994 (5.7 MBs)

Japanesse

1996 (2.1 MBs)

German

XTR Only

2006 (9.1 MBs)

German

2010 (15.0 MBs)

Spanish

** thank you to Vintage-Trek.com

Sheldon brown has good Shimano info here

Mombat has info on XT and XTR here