I know little about aftermarket exhausts because I have no interest in them, but you're suggesting that the EPA regulates stock mufflers but ignores the aftermarket? I would think the aftermarket products would need to conform with EPA rules and use "EPA pieces", but again, what do I know?
When I investigated aftermarket exhaust for my Royal Enfield I discovered a neat little trick the manufacturers play. The aftermarket exhaust are noted ‘for off road use only’ in which case they aren’t subject to the same EPA regs. This is why most of them are shorter, louder and more free flowing. If you get caught with one then it’s on you because the makers TOLD you not to do it. Just the little bit I learned.
