In my experiences, I have never seen a "mail train" or "express train", that did not have the rider coach/combine attached to the rear (the exception of course would have been the PRR, that had so many mail & express trains that they finally outfitted N5 cabin cars with higher speed trucks and steam train lines for steam heat inside the car, and those cabin cars were lettered & assigned to "Assigned to Railway Express Agency).
As added information, the Southern Pacific operated an over night PFE reefer train with a three digit, low number, train number (being a second class passenger train) usually pulled by a GS class 4-8-4, with a coach in the rear. Even though the entire train was made up of all ice refrigerator cars, passenger could still purchase a ticket to ride the rear coach, in the middle of the night.
