I think 00 is the earlist you can go, when I got my slip in it said 2000 zx6r. I don't think they are the same but I never looked into it.
The best thing to do is to find a exhaust site and see how they group the years, if there a different part numbers for differents years then 00 and up are the only pipes available for you.
The best thing to do is to find a exhaust site and see how they group the years, if there a different part numbers for differents years then 00 and up are the only pipes available for you.