I'm looking at doing some basic bolt ons to my GSR and I see several sites that list parts will fit only 94-99 GSRs. Mine is an 01. What are the differences in the 99 and the 01 GSR that would make these parts not fit?

For example, I'm looking at putting on a Comptech High Flow Catalytic Converter and Comptech lists only 94-99 for this cat.
I also see some suspension components are like this as well.

Any ideas?