Just curious why it is that some Lionel 6822 cars came with both a fixed coupler on one end and one operating coupler on the pickup side? Other 6822 cars I've seen have operating couplers on both ends. Did it depend on wether it was sold in a set or sold separate...color of car

Anyone know ? Thanks
My understanding is such variations are explained by manufacturing decisions from one year to the next, based on parts availability.