Valvegear,
Once a very common term, as 'the railways' had at some time in most or all jurisdictions, been an actual govt dept with a Minister for Railways ruling over the dept.

Any Victorian crew who attempted to disable the V.C would not have lasted long. The Hasler Speed Recorder made a record on a chart, and recorded speed, time of day, time travelled and at stop, and distance travelled.

VR report, para 5.3.1: " There is provision on the chart for other readings, and in Victoria this is used for recording the operation of the Vigilance Control System."

VR Report, Section 9, "DISCUSSION", has details of when the V.C. was pressed, and at what distance ( in miles and chains) from Melbourne. The final actuation was at 105 miles, 20 chains, which was within the Violet Town Loop.

"There was a time interval of some 54 seconds from when Fireman Coulthard first saw the Home Departure Signal at Stop to the point of collision, a distance of approximately 1 mile and 5 chains."

"The tests of Westinghouse Brake ( Australasia ) Pty Ltd showed that this train could have been stopped in 48 chains if an emergency brake application had been made from the locomotive, and it is difficult to understand why Fireman Coulthard did not take this action."

Certainly not common in my 74 year life time, with a father who was a Rolling Stock Engineer. It was commonly "Victorian Railways".

The sequence of names is:-
1857 - 1871 Department of Railways.
1871 - 1877 Department of Railways and Roads.
1877 - 1884 Department of Railways.
1883 - 1973 Victorian Railways Commissioners.
1973-1983 Victorian Railways Board.

I remain surprised that the term "Railway Department" was used in an official report in 1969.

 How did the Hasler speed recorder know the precise location of the train back in 1969, please?

It was set at zero and signed by the Driver before the journey commenced. Distance at start was zero, and distance travelled was easily recorded, just your car's odometer does. In the case of an Up train distance travelled subtracted from total distance from start (zero) to Melbourne gave the location in miles and chains from Melbourne. In other words, the start is 185 miles from Melbourne, and this is set at zero. The train has gone 85 miles on the chart, so it is 100 miles from Melbourne.

A skilled reader can get very accurate distance measurements from a Hasler tape. The speed indication is very accurate, as is the time stamp.

It never ceased to amaze me that when an incident occurred such as this or someone was hit by a Train, the Guard was 'grilled' more extensively than the driver.
On paper at least, the Guard is the employee in charge of the Train (NSW) and not the driver yet most events were at the front of the Train in many cases out of the sight of the Guard, not the rear where he was.
I remember a Guard of an Interurban heading to Sydney one day when it hit a 'Jumper' at a station out near St Mary's/Blacktown and he told he had just come from the Inquiry and he had spent quite some time being questioned where as the Driver barely gave his name, employee number etc and was gone.
The Guard was asked what speed the Train was doing, as if he would know as he has no speedo to read along with some questions which inferred he was at fault and wasnt doing his job.
From memory there was almost no forward view along the train of those first single decker Interurbans unless you opened either the door or window.
Just before the ultimate removal of the Brake Vans off Freight Trains in NSW, there were experiments carried out to improve the forward view, such as a raised 'hatch' area fitted with mirrors so the Guard could see forward from his seat at the desk because Trains were growing longer and longer.
I only ever traveled a few times in a Brake Van and sat trying to look along the Train which between Penrith and Bathurst was a waste of time as you could rarely see more than a quarter of the Train for most of the journey.

Prior to this happening at Violet Town, I would be very surprised if any Diesel Loco's in NSW were fitted with any sort of Vigilance control.
The only such control as I remember was the "Dead Man' handle fitted to electric Suburban and Interurban  passenger trains.

They served great coffee in the buffet car

Southern Aurora did not have a buffet car. There was a full scale dining car and a lounge car only.
SoP (Spirit of Progress) and Intercapital Daylight both had a buffet car.