In reply to jkarran:
Batch codes from 1988: Example 1Y : 1 = Month January Y = Year 1990
Year 1988 batch codes 1W - 12W
Year 1989 batch codes 1X - 12X
Year 1990 batch codes 1Y - 12Y
Batch codes from 1991Example Z01 : Z = Year 1991 01 = Week 1
Year 1991 batch codes Z01 - Z52
Year 1992 batch codes A01 - A52
Batch codes from 1993 Example 842 : 8 = Year 1998 42 = Week 42
Year 1993 batch codes 301 - 352
Year 1994 batch codes 401 - 452
Year 1995 batch codes 501 - 552
Year 1996 batch codes 601 - 652 Important Note - Nylon Stem Cover Introduced
Year 1997 batch codes 701 - 752
Year 1998 batch codes 801 - 852 Important Note Coloured Cams - Red only Introduced.
Year 1999 batch codes 901 - 952
Year 2000 batch codes 001 - 052
Year 2001 batch codes 101 - 152
Year 2002 batch codes 201 - 252
Batch codes repeat from 2003 onwards, i.e. 2003 Friends start 301, 2004 start 401 - and technical changes, such as stem cover, able us to identify a Friend made in 2003 from one made in 1993 although both would carry the 301 - 352 codes.