It seems like putting together a puzzle with pieces of collected information, and you never know what bit of information might cause something to click for someone. Rob John could say if anyone made improvement on Ark's material in between seminars. In other words there are probably a number of people who saw him twice, with a year in between.
As much as I understand Dan H's pov, there have been times where I've seen Ark pleasantly surprised by people's progress, without mentioning any names, especially considering the fact that they only have long distance access to us.
Putting it in another light,
Ark only had personal contact with his own instructor for a period of two years, and even then it was once a week if he was lucky, but more on the lines of once every two weeks.
Granted, it was a deeper study than what you would probably get in any class, but the point being that for the most part I have the impression that he had to study and think on his own for the most part.
And we have students that come pretty much every week, but still don't get what they're supposed to be doing...so it goes both ways.
Honestly I think it boils down to two factors, most people dont think hard enough about the stuff, and don't put in the practice time.