Just a guess, but perhaps they switched more cars on the back-end and only NG on the front, thus not having to mess around with the adjustable coupler.
Also they could switch SG cars from the other end with the dual couplers, so they could grab stuff from La Veta from the back and sort it, then go around the other side and switch NG cars. The NG couple would set-up for switching trains making up for the trip to Chama and the dual end would be used both ways for breaking up a NG train, and setting up the SG one perhaps. Maybe over-thinking here.
Greg