Oh of course, maybe I should have mentioned. In Gen III the pokedex order in the game files is completely different to what you actually see in game. 1-251 are as expected. Then there are 25 empty slots. Then treeko is 277 (I think 0x115 in hex). However the ordering of the hoenn pokemon is also jumbled a little. Use this list Bulbapedia's List of Pokémon by index number (Generation III)