Interestingly, in the case of those two, the one who was more diligently and recently practiced failed on day 1, while the other who hadn't dived for a year and left preparations to the last minute made it to day 5.To fail (essentially be dropped by instructor) on day 1 means the student was completely unprepared for the course and would have slowed down the progress of all other students.
In the case of the first I think it was one of the first tech passes the fundies instructor handed out so it was a learning experience for him too.
Something else I found out is that GUE instructors can look up their student's past instructor feedback. When I took my tech upgrade I was mortified to hear "so leon said you have poor situational awareness" Instant flashback to my first fundies class not noticing my buddy getting entangled during ascent, the school of sharks in a swimthrough everyone saw except me, etc.