Let's apply what is currently done for air transportation to rail transportation. If a plane were to crash at take-off or landing, the carrier would definitely not go before the courts to argue against the victim. Obviously the passengers would not be at fault. The same would apply in cases of train collisions or derailments.
I gave you a hypothetical intrusion example, someone putting themselves on a train track. In that case there would be a trial in order to determine whether or not the victim was responsible. In the case of the Lac-Mégantic disaster, the carrier absolutely cannot argue that the victims were at fault. Therefore, there should be no question of deadlines for challenging payment of the first portion of compensation.