>It's interesting that no one discovered the Midway base in four
>hundred-odd years. Earthforce and/or Black Omega clearly have
>some line on leftover bits of the fleet (it seems like Kongō
>didn't know about it, which is curious in itself since she was
>presumably constructed there, but still) and there's surely been no
>shortage of treasure hunters and so on, in between the end of the Fog
>War and the present day.
Given the memory loss that the other ships suffered, Kongō might have had a similar problem, so she wouldn't remember where she was constructed. It's also possible that she was constructed elsewhere.
As for treasure hunters, what reason would they have to search there? Fog stealth systems are probably more than capable of hiding the fact that the entire island is hollow, even against 24th-century technology, and it's likely that nobody would bother scanning them anyhow.
Insert humorous comment here.