I think it's a common mistake. It would be much more intuitive for the one literally labeled "two" to come after; I imagine it doesn't work like that because they wanted the mythical one last.
Mew wasn't supposed to be in the game at all. Only as a special event in Japan. Mewtwo, Articuno, Zapdos, and Moltres are all mythical / legendary. Mew was added to the Pokedex because they had just enough memory left at the end of development.
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I think it's a common mistake. It would be much more intuitive for the one literally labeled "two" to come after; I imagine it doesn't work like that because they wanted the mythical one last.
Mew wasn't supposed to be in the game at all. Only as a special event in Japan. Mewtwo, Articuno, Zapdos, and Moltres are all mythical / legendary. Mew was added to the Pokedex because they had just enough memory left at the end of development.