Sevii Islands 8 and 9

From Glitch City Wiki

Within Pokémon FireRed and LeafGreen, additional data exists for another few Sevii Islands, labeled as 8 and 9 and do not appear at any point in-game and are henceforth not accessible.

However, as compared to other, similar additional Sevii Island maps (such as a second 6 and 7, ones labeled as 22 through 24) 8 and 9 are shown to actually have map data of their own, but are primarily featureless (with somewhat of an exception for Sevii Island 8, which does have what was originally a cave entrance which had its entrances hastily edited out). Both maps do not have any Pokemon nor NPCs programmed and are typically attributed to as being abandoned map data left over from previous alpha/beta versions of FireRed and LeafGreen.