I don’t remember exactly the reason I was told, but IIRC it has something to do with typing ‘n’s on JP keyboards… I think you have to hit the key twice or something. There’s another spot where it’s mistyped as Ninntenndo, so that may be the reason, or maybe their keyboard had a sticky n key :-P.
The game seems in excellent condition, congratulations. I think the Ninntenndo typo was on the cart, but I’m not 100% sure. I’ll check it as soon as I can. Anyway, enjoy your collection. I know it’s a great feeling every time you increase it 🙂
Yes in Microsoft IME you have to type the n twice to get ん. It will automatically convert it if ん is not followed by a vowel (a, i, u, e, o). If followed by a vowel, the IME would obviously convert combinations of the vowel with n and not ん, な、に、ぬ、ね、の. It is therefore not really needed to type ninntenndo for にんてんど.
However, it seems many Japanese type nn regardless.