Shimano dates their components. On the older parts, there are stamps, on the newer parts there Are some little round sticker in silver.
Here is the key :
1976 - A 1977 - B 1978 - C 1979 - D 1980 - E 1981 - F 1982 - G 1983 - H 1984 - I 1985 - J 1986 - K 1987 _ l 1988 - M 1989 - N 1990 - O 1991 - P 1992 - Q 1993 - R 1994 - S 1995 - T 1996 - V 1997 - w 1998 - X 1999 - Y 2000 - Z 2001 - A 2002 - B
and for the months :
January - A February - B March - C April - D May - E June - F July - G August - H September - I October - J November - K December - L
Thomas Reitz
Wiesbaden, Germany