As I had mentioned to another Prime Member who PM'd me - I do not know if it will fit any other years past 96, I have heard that other exhausts similiar to this one fit 91 - 96 and there was a change for the 97's and on, maybe it would need an adapter, I wouldn't be comfortable selling it not knowing for sure.
Here is some info from Science of Speed who sell adapters as well as other awesome parts for the NSX:
The piping design of the NSX exhaust behind the catalytic converter was changed by the factory in 1995, and again in 2000.
1995-1996 factory exhausts use the same design as the early cars with the addition of adaptor pipes between the exhaust and converter. In 1997, these pipes were integrated to the exhaust design. In 2000, the design changed slightly again. To install an aftermarket exhaust, 1997+ NSX owners must use these adaptor pipes to correctly fit the exhaust. 1995-1996 owners may use their factory adaptors. However, since the factory pipe diameter is smaller than aftermarket exhaust and headers, we recommend customers with these cars to upgrade to these pipes for maximum unrestricted airflow.
Sceince of Speed Link: