I confess...

After over 30 yrs on the planet I only just learned that Harry is short for Henry apparently. How the fuck does that work?

Heno maybe. Not Harry. That being short for Harold makes way more sense.

Either way I can't believe I didn't know that.

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