Taken from a recent Iwata ask:

Tanabe: What? Really?

Wada: No one has known about that for about 22 years…

Everyone: (laughter)

Wada: I was wondering when I would have a chance to tell people that.

Iwata: You’ve been holding that information for 22 years since the release. (laughs)

Wada: Now that I had the chance. (laughs) There are a lot of hidden elements in the NES version.

Full Thing HERE