JP, Cazatou
Yes, it is true that at least one of the Air Marshals told the HoL Select Committee that negligence had already occured before the waypoint change. However, so far as I can recall (and I am willing to be corrected), that was the first occasion such a statement had been made in any "public" forum, including the original review comments on the BoI.
It seems to me that a prerequisite for alleging negligence is to be able to state what was done (or omitted) that may have been negligent, and also to identify either the time or the place (or both) where this act or omission occured. The importance is that it is necessary to understand what were the exact circumstances pertaining at the time, which would influence one's view as to whether an action was truly negligent, rather than an error of judgement, or indeed whether it was excusable in the circumstances.
On those grounds, in my opinion, the loose description of "sometime before the waypoint change" is simply not enough to support a finding of negligence, and especially not of negligence to a gross degree.
Regards
Ginseng