Hey guys. I ran into a Surskit and Roselia once on Pokemon Emerald, although I was unable to catch them because I had just recently started the game at that time. Now that i've finished the game.. i've finished it a while ago but that's not the point, on the Pokemon Emerald Hoenn pokedex Surskit and Roselia come up as unknown locations yet I ran into them. Can someone please explain how this kind of thing happens?
Yes it is possible. Often Pokemon are obtainable in different ways (e.g. gifts or fossils) so they don't show up on the in-game map. In your case if you were walking around in grass they must have appeared due to a swarm.