So you're fine then. When a cop pulls you over for having exhaust that is too loud recite this little snipet of info and see what he does. It's being a pain in the @$$ but he shouldn't be writing tickets that he can't prove. I say borrow a criminal code book, or search the net for that section, print it out and bring it to the court date.

What you could do to better your "case" is use a dB meter at 50ft and videotape it to show them how loud your exhaust really is. Obviously the meter won't be calibrated either but nonetheless, it should work.