It's basically country-wide now. That's the reason DT headers and Borla exhaust etc are on such long backorder or discontinued. The EPA issued new guidance a few years ago and fired a shot across the bow of all aftermarket companies. They hit the biggest offenders with several million dollars in fines. The EPA states that CARB exceptions can be used to prove compliance nation wide.
A cat back exhaust or headers do not affect emissions from a vehicle, but unfortunately now the onus is on the manufacturer to submit to testing with CARB or EPA to prove that it doesn't. Basically if you are Borla or Magnaflow etc they just ruined your business model.
The EPA Enforcement Policy on Vehicle and Engine Tampering and Aftermarket ...
https://www.epa.gov/sites/default/f...orcementpolicyonvehicleandenginetampering.pdf