Educated guess only…
This is a one day event. They’re going to run each train exactly once, from one end to the other.
If you do what most people do, and ride from one end to the middle, and back, you’ll swap locomotives in the middle.
If you ride one end to the other, you’ll stay with the one you started with.
Whether or not that qualifies as “Great” I’m not sure.
Matthew (OV)