what are you talking about?
you act as if you never knew how the console worked.
unused slots are not "missing" firmwares.
the loader only use ONE IOS at a time, and it's usually the one in slot 249.
having, or not having, any other IOS slot is completely irrelevant to compatibility. and it's the same with their base or version of all unloaded slots.
I suggest you read the guide I'm writing here to learn how the console and homebrew are working:
https://gbatemp.net/threads/wii-hacking-explained.501605/
specifically from the chapter1/IOS section.
try not to suggest wrong things to users, you'll make them do unneeded or even useless changes, but more importantly you'll make them think they have a problem and they need to worry about it, while they don't.
people who want to use USBLoaders only need ONE, and not more, cIOS. usually, v8 base57 is all you need. nothing more.