I offer this more as info than anything else, but history is full of trains building at the platforms, sleepers could be set off in mid route at the dead of night, and some trains set off Dining Cars rather than dragging them around, for other trains to take them back the other way. And on top of that, some trains ran with multiple sections, they might leave Point A as one train and then at Point C the first third of the train and one of the engines splits off the other direction.
Amtrak ran the FLoridian from Chicago south. there were 2-3 engines, as needed Head End Equipment, then a sleeper, a Cafe, and then the coaches, a Dining Car, and more sleepers. Once they got to Florida, They sawed off an engine, a baggage car, and the front sleeper, Cafe, and coach(es). There was a transfer (frieght) yard to do it in, but it was a long way from being in a Coach Yard.
The Texas Eagle pulls a similar trick. In San Antonio, they whack off the last two cars, a Through Sleeper and a Coach, and tack it onto the Westbound Sunset Limited, flipping the two in positioning so the Coach passnegers don;t have to walk through the Sleeper.
So, plenty of reasons to switch Passenger trains on the road. :)