When and why did Mickey change to Miki (Dora)

I have done some extensive research in this topic and have found on page 87 of SURF FEVER that indeed at some point Mickey Dora became Miki Dora. With all of my research I can’t figure out when it happened or why it happened. The old school way seems to go with Mickey and today it is spelled Miki. Is there a story Im missing? Thanks for your help.

if anything, i’d have figured it went from miki to mickey – trying to make it sound more american (there was a surge of patriotism back then when foreigners were considered evil…sound familiar??). maybe after people got real he wanted to get back to his roots and started going with miki again.