Okay this is for GTS 6 Speed mind you....
2000 - Original Spec
2001 - Corrected Logic for faulty P0300 detection
Late 2001 / 2002 - Lowered Rev limit to 7800 RPM, 2002 also saw the introduction of teh 2 wire "flat type" knock sensor
2003 - Introduction of drive by wire and re-instatement of 8300 or 8400 Rev limiter (have not tested myself to determine exact point)
Parts Timeline
08/16/99-9/7/99 - 89666-20080 (Very limited production, does not show in parts catalog or on parts master but does show in computer system. as having been used for a short time. Can NOT be ordered)
08/99-12/99 - 89666-20081 (subs to the 20082 number in the parts system - because of that there is 0 stock and it cannot be ordered)
12/99-08/00 - 89666-20082
08/00-08/01 - 89666-20083
08/01-08/02 - 89666-20190
08/02-10/02 - 89661-2G400
08/02-current - 89661-2G401