US Blue is Japanese Green. You see, in Japanese Blue some of the Pokemon you couldn't find in the wild in the first games were available. For example, Jynx can only be obtained through an in-game trade in R/G. In Blue, it can be caught in Seafoam Islands.
Don't ask me if Blue had Mew, because it obviously didn't (anyone can get Mew in Japan, they just go to the "Pokemon Center" stores in Tokyo or Kyoto and get it downloaded into their games).
IIRC, in Japanese Blue, PP Ups were buyable. Correct me if I'm wrong though.
Now, as I've said before, our Red and Blue is in reality Red and Green. But NoA used Japanese Blue for some cosmetic changes to our games ...
The Pokemon image graphics in our Red and Blue are from Japanese Blue.
The intro to our Blue is from Japanese Blue.
The Pokedex info in our Red/Blue is from Japanese Blue (therefore, Japanese R/G has untranslated info, but what I want to know is, why didn't NoA put the R/G info into say, Pinball?).
And the Unknown Dungeon in our R/B is from Japanese Blue.