I went back and check through a lot of the trainorders and line-ups I have for the early 60's. While a lot of trains ran through with two engines, I also found lots of evidence of engines running light to Gato from both Durango and Chama. I guess it depended on where the engines were and the tonnage of the trains. Apparently if helpers were running light to Gato from Chama, the standard practice was for them to run 15 minutes behind their train. What I could not determine was if a helper from Chama assisted its train to Azotea, did it run to Gato ahead or behind the train.
Running ahead in both cases would seem to be easier, but perhaps there were issues that trumped the need to throw a couple of switches.
JBWX