So...I was reading the Iwata Asks: Super Mario 25th Anniversary interview, which I could have sworn I read, but apparently I didn't because if I did, I would have remembered this very important little tidbit:
http://iwataasks.nintendo.com/interviews/#/wii/mario25th/4/0
Mind blown. Now some might not think that sounds very impressive since SMB is relatively speaking, a fairly simple NES game. But keep this in mind, both SMB3 and SMW each took 3 YEARS to make. So in a way, the development time for SMB is kinda badass.
Nakago: These are Miyamoto-san's first specifications for Super Mario Bros.
Iwata: Oh, this is in the booklet included in the Super Mario All-Stars Limited Edition package.
Nakago: Yeah. We still wrote them by hand back then, and the seal is from the Creative Department.
Iwata:That's the seal for the section that existed before the Entertainment Analysis and Development Division, and the date is...February 20, 1985. That means it was written the same year as the release of the original Super Mario Bros.
Miyamoto: We wrote the specifications on February 20, and six months later we put it on the ROM...
Iwata: That's fast work! (laughs)
http://iwataasks.nintendo.com/interviews/#/wii/mario25th/4/0
Mind blown. Now some might not think that sounds very impressive since SMB is relatively speaking, a fairly simple NES game. But keep this in mind, both SMB3 and SMW each took 3 YEARS to make. So in a way, the development time for SMB is kinda badass.