From Bulbapedia, the community-driven Pokémon encyclopedia.
Sevii Isles 8 and 9 are locations which are not accessible through normal gameplay in Pokémon FireRed and LeafGreen. However, unlike other similarly-named unreachable areas, they have actual map data.
No Pokémon are programmed into the areas by default; it seems as if there are abandoned areas left over from the Pokémon FireRed and LeafGreen beta. No index pointers lead to it by default either; on Isle 8 the central island of the "route" has what one would assume to have been cave entrances changed into the side of a rock.
If it is entered when walking on land, it has the same route theme as the later Sevii Islands routes.
There are also maps programmed in the games for "Sevii Island 6" and "Sevii Island 7" in addition to the versions in the final game (Six Island and Seven Island). However, they have no map data.
