Tail lights
Tail lights
I'm not entirely sure when they changed the rear lights, but it was around 2003. Later models had lights with rounded bits at the bottom and the earlier ones were flat.
Flat model:
Rounded:
The later model rear lights can be fitted to an earlier model WRX, but if your car came with the flat model tails you'll have to modify your rear bumper a little bit or it will be slightly pushed down by the rounded bit.