I confess...

here are some more from: http://www.moonzstuff.com/articles/nicknames.html

Strange Nicknames. Not all nicknames are obvious. For example, Polly, Patsy, Peggy, and Nancy are actually nicknames for Mary, Martha, Margaret, and Ann, respectively.

with the exception of peggy = margaret, which i knew, those are mindblowing

My Grandma Margaret was of course known as Nancy!! as thats how Margaret was shortened round here, just to simplify things.