Some of these I understand, or at least am used to. Bill for William, Dick or Ricky for Richard, Bob for Robert, etc.
However, Jack for John, Ted for Edward, Betty for Elizabeth, Peggy for Margaret? I haven’t encountered any if these. Ted for Theodore, Ed or Eddie for Edward, Liz or Lizzy or Beth for Elizabeth – those I get, but the aforementioned just make no sense.
Oh, and Polly for Mary? What the hell is that? Not only is it not similar, but the nickname is longer than the full name. Craziness…