I know he has been around for a long time. At 1st his org was called the Midwest TKD Association in the 1970s. I would imagine that he trained at a time with a Korean who was affiliated with doing the ITF Tuls, called hyungs back then. Whether or not that instructor was a member of the ITF & issued ITF certs is another story. I do not think that GM Benko himself was a "card carrying" member of the ITF & yes the ITFers do have cards to show that they are ITF. He may have had an ITF BB cert or 2, but not sure. I would gather that once he had his own org & that was decades ago, he remained independent. I do know that he did met Gen. Choi at some point years ago. Not sure if they tried to get him to join. It was possible that he just attended a training session(s), just not sure.
I personally never saw a need to get his training manuals, as they would have had little benefit to me, as I follow the 15 volumes. I will google that instructors name.