Originaly there were meant to be 48 Colossi to battle but because of software limitations it was cut down to 16. Despite this, 7 other Colossi were partially programmed into the game
several Generation 2 Pokemon were meant to be part of the first games but were due to time restraints, because of this there are numerous versions of the Missingno. glitch as well as why some Gen 2 Pokemon are seen throughout the first season of the Anime