In the most recent Iwata Asks interview Wada discusses the original game and, since he has the chance, reveals the secret. “This is a great opportunity, so I have something I’d like to say. In Punch-Out!!, the game gives you a lot of hints about effective timing of punches. There is a big boxer called Bald Bull in the NES version as well and a light flashes to the right in the audience when he charges. If you punch when it flashes you will land a body blow” he said, going on to claim that this was the first chance he had to tell his secret. Not only this but he goes on to say that there are “lots of hidden elements in the NES version.”
via Destructoid