In pokemon diamond how do you get the pokemon to appear in your pokedex?

I have 256 pokemon and when I play on wi-fi the pokemon I encounter don't show up in the pokedex. I've encountered almost all the pokemon in the map . Plus where else can I go in pokemon diamond. I've been to stark mountain and sendback springs and the snow temple. Any suggestions?|||you have to either battle them or catch them.|||maybe you already have them, you want to try a legendary and if that dosent come up well... your game is screwed