this is the explanation. first of all, Krist is his original croation spelling, which he went back to around 93. as for kurt. when kurt was setting up the session for the first demo with Jack endino over the phone, jack had no idea how to spell his name so he wrote: "Kurdt Kovain" on a sticky pad. Kurt saw that and thought it was funny. so he started crediting himself as Kurdt Kobain on a lot of the band's releases. part of this may be due to inspiration from bands like TSOL and the Adolescents whose members changed their name on every album.
example:
TSOL lead singer Jack Grisham has been credited as: Jack Greggors, Jack Lloyd Jones, Jack Ladoga, Alex Morgon, and Jack Ledauge