Punch-Out!!!, the latest edition of Iwata Asks is chock-full of tidbits about the game that you probably didn't know. For instance, Nintendo Entertainment and Analysis Division's Makoto Wada reveals a long-hidden secret that makes fights against Bald Bull go much easier. Also, Glass Joe? He's got osteoporosis. Yeah, you should feel bad. Poor guy.
However, the most entertaining unearthed secret is the fact that Shigeru Miyamoto never signed off on the use of Mario as the game's mustachioed referree. In Miyamoto's own words, "we didn't have an approval system when using Mario images back then and it went right past my check." The interview transcript adds that he laughed after saying this, but we imagine at least one stink-eye was shot across the table.