Other key questions.
Who was this Fay Keely, apparently the owner of the aircraft ? Why did they buy it ? Were they current on it ? Was it just for their private use, and if so what records are there of them using it themselves ? The Malibu is a large aircraft for someone unknown to have just for their personal and private use. Were they not equally in it with Henderson ?
Separately, and something I have asked before, why charter in the first place, at considerable cost. There was a commercial KLM connection, Nantes to Amsterdam, and then nicely Amsterdam to Cardiff, at pretty much the same evening times as this charter was operating. If the football player "had to be back" for the following morning, that was the obvious way to go. The cost of even a business class one way ticket would have been a fraction of the charter cost, and much more comfortable and reliable.