I've had a new 250 every year since 98, other than the forks and triple clamps parts are interchangeable, the motor is basically the same all the way to 03, different porting and head configuration, CDI and ignition may be different as well. the pipes will work on those years as well, they are slightly tuned different to match the porting. I ran an 00 pro circuit on my 01, it pulled harder out of the corners. brakes pads, discs, wheels, rotors, swingarm (250 only 125 shorter), plastic, seat, pretty much the whole bike. Even though the part numbers won't necessarily cross most parts are interchangeable with your 99 250.