I think there are a bunch of encodings that just repurposed a few ASCII characters as different characters - someone on this page was giving the example of some

I think there are a bunch of encodings that just repurposed a few ASCII characters as different characters - someone on this page was giving the example of some Swedish encoding where {}| were replaced with three accented Swedish letters. There are probably a bunch of others. In those cases, the text will decode fine as UTF-8, but it will display the wrong thing.