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Additional Kiki's: Ruth Bader Ginsburg went by the nickname Kiki in her youth, and Kiki is the main character in the film Kiki's Delivery Service by director Hayao Miyazaki.
Cecily and Blythe are also familiar names from the Anne of Green Gables books.
I don't see how Brett is "undiscovered" since it was quite popular in the '70's. I also know a few Mitt's, short for Mitchell.
I know a Fritz (on the fritz would rule that out) and a Franz.