Rob is short for Robert, Bob however is also short for Robert and not for Bobert or even Borert. Rich is short for Richard, Dick however is also short for Richard and not Dichard or even Dicharr, Rik and Rick also are short for Richard but not Rickard.
Rickard, Dichard, Dicharr, Bobert, Borert are not it is said, real names, however the same I suppose could once in the deep bowels of time been said for Robert and Richard.