That most recent link says the Vaughn couple did witness the actual crash point of impact as they were approaching the crossing, so my previous speculation is inaccurate. If the vaughns did witness the actual impact, the flashers and gates should have been activated at that point, and prominently visible to them. Yet they say they saw no activated signals or gates.
I assume that the Amtrak locomotive video that is said to show the flashers and gates working also shows the vehicle approaching and being struck, so there can be no doubt about which day the video was taken.