Having operated quite a few "fuel critical" sectors in (subsonic) aircraft, it can be very tempting to "gild the lily" when it comes to fuel on board and observance of the RTOW rather than risk an enroute fuel stop or being on minimums at destination. Had this become a common practice?
What was the weather/delays like in JFK on the day in question?
How was the Zero Fuel Weight (sorry Mass) of the aircraft computed. Were assumed weights for pax and handbaggage used?
On one aircraft I flew we made regular flights to a destination which was critically landing weight limited. We decided to weigh all hold AND hand baggage to ensure compliance, rather than using assumed weights.
Were the passengers on the AF Concorde "normal" in terms of weight, etc?
This would be yet another factor to add to the issue of being, allegedly, over the RTOW.
None of my comments are intended to cast any aspersions on the crew who must RIP.