They went from AWW/AWD engine code to AWP, the change was just a little more boost from a KO3 sport instead of the regular K03 on the earlier years. Also the early years were underrated by VW, so when VW came with the 24V VR6 rated at 201 they could up the HP on the 1.8t, basically VW didn't want the 1.8t to steal the VR6's market, since the VR6 was the "higher" model. All of the 1.8t's respond to the usual mods the same, so if you plan on modding it, it won't matter what year you have.