Wii game prompts for update even though the System menu is newer than the one on the disc

I softmodded a friend's wii, and went from 3.3 to 4.1 using this guide. I tried inserting Mario Kart Wii (original), which wouldn't run unless I ran the updater on the disc. It worked with the old 3.3, why would it do this with 4.1?

Apparently the game checks a whole lot of IOS that it needs in order to run, and if even one of them is missing, it prompts for an update (which will probably damage the wii, since it "updates" to an older System menu). I found many lists of games, along with which IOS they need in order to run; but I checked and all of the needed IOS were installed.

I tried Mario Kart Wii on my wii, and it was fine (I had followed the same procedure to upgrade/softmod mine), thus I ran AnyTitle deleter and compared the IOS installed on both wiis. The culprit was IOS14, it was present on my wii but missing from my friend's (but none of the lists I found online mentioned that IOS14 is needed for Mario Kart). I installed it with the help of Dop-IOS MOD. It worked, the update prompt disappeared and Mario Kart Wii was launched.

I know this is quite a specific problem; unlikely to happen to someone in the same way. I'm hoping that this post will help other people figure out why they're getting an update prompt even though their System menu is newer than the one on the game's disc.