A note on transport Canada and Canadian Railroads rules they were different not pro company in the case of Transport of Canada again rules changed as circumstance change . Some of the Canadian railroads operations practices and management pressure from above were the cause of some of these incidents. The on the ground train crews many times reported issued with with PSR were ignored.

As to the evolution of the Brake equipment yes the ABD came out in 1964 and has been modified and now there are other variants out there. One of the things the ABD valve did was to add a quick release feature that has been enhanced over the years and truck mounted brakes also have made a difference. Back in the day bottling the Air on a cut of cars was legal and condoned on some railroads . What is bottle the air, Closing the Angel cock on both ends of a cut of cars with the air set and with the old AB brakes they may stay set for a long time,
With the advent of the ABD brakes and QuickClips release if you bottle the air to quick and the air bounces back into the train line you get a wave of air which could cause them brakes to start releasing an d as they release with the quick release feature more air is added to the train line from car reservoir which adds to the wave and more brakes start to release and then if there are no hand brakes the cut will roll away. That’s why it is important to tie hand brakes before you cut away and not potted the air and do a pull test per FRA regulations too see the cars stay put.