But all the indications are that the loop started at below 500 ft, why, what was the margin for error?
Concerning "margins for error": what is the margin for error for identifying the maneuver as a loop. A loop is done in pitch axis only and the tragic maneuver included pitch and roll. So given that you don't know what the intended maneuver was, how can anyone judge what the margins were, much less which ones were violated?