How come misono and Koda Kumi have different last names?

[matt]

This could have something to do with it. Or maybe not.

The kanji Misono uses can actually be read at least 2 ways: 'kanda' and 'kouda'. And as we know, when romanised Japanese tend to drop the extra vowel giving you 'koda'. Anyway, this could perhaps be a way for one of the two to more or less keep their original name in some form, yet have that difference by changing the pronounciation and kanji.

Or, it could be something totally different.