"Kurt Cobain's "alter-ego". He used it when he wasn't feeling himself."
"How he actually spelt his name, as seen in his own journal."
"The spelling Kurt Cobain sometimes used to write his name, as appears on the back of Nirvana's first album 'Bleach'. His middle name was Donald, which I think displays Kurt's eccentric sense of self."
"Kurt Cobain spelled his name sevreal different ways for no apparent reason. The odd spelling Kurdt came from when Nirvana recorded “Mexican Seafood” for the “Teriyaki Asthma” compilation. When it came time to make the album, they realized that they didn't know how to spell Kurt's name so they got a ..."
I don't know. Those are some results with Google. You can find the sources by searching the quotes.
I was never a big fan although I hung out with Eddie Vedder on the beach back in the late 80's while Kurdt and Chris Cornell hung out in the hotel room in Maui