Well I bet "don't call me Joey" Albert Belle wouldn't sign a card with Joey. And Giancarlo Stanton didn't sign many items "Mike".
Why would a player sign something with anything but what they preferred to be called?
I've heard Roberto Clemente being called "Bob" Clemente, but most of the time it's always been "Roberto". Maybe Roberto saw a HUGE line of people that wanted his autograph and figured he could get through the line faster by signing them "Bob".
I have less faith in TPG authentication of autographs than I do with TPGs subjectivity in grading of cards.