I imagine the unions didn't care too much as long as no one lost any work by another craft doing the work. There was quite a bit of craft-crossing where brakmen would fire and fireman would work as brakemen as needed.
Durango was feast or famine location with lots of work in the summer, and not enough for even one crew in the winter - especially in the mid-1960's after they began shutting the NG down in the winter. That's why guys like Steve Connor and Bill Holt moved back and forth between Alamosa and Durango. They had enough seniority to hold a job at either spot. Connor lived in DGO but went to ALA when work got slow in DGO.
There was still a switch job in Durango through 1968. The top engineer got that job - assuming he wanted it. The next four guys got the Silverton Train. When a train got called to go east, The #4 guy got that call and if a doubleheader went east, #5 went out. That created a vacancy for firemen to Silverton, as well as firemen were needed to go east. Up through 1967, trains ran every 7-10 days, and they kept the extra guys busy, working freight trains and doing hostling jobs.
Once the Silverton Trains came off in the fall, the work got scarce for the lower guys. In Dec, the last freights ran until spring, and most everyone was out of work. The older heads were forced to go to Ala or Pueblo to work. Some trainmen went to Grand Junction as well. Payne was the only guy to spend the winter in Durango, getting unemployement, waiting for spring.
There was some sort of "Mileage Equalization" thing for enginemen in that if they were on in a pool and for whatever reason they didn't work as much as others, they would get run around a more senior crew man to get more work. I know they did this in Alamosa, not sure about Durango.
The Silverton Trains were a 7 day/week job. If you signed on for it, you worked every day, unless you made arrangements to lay off. It must have been brutal. By the end of Sept, you had to have been burned out, cranky and really tired of looking at the same jerk across the cab from you every day.
When Kyle Rys. went to a 7 day/week operation on the C&TS in 1982, the initial thought was to simply work us every day "just like they did on the Silverton Branch".... One guy, George Knauff, was retired and about 60 something years old. He flat refused to do it. So they gave him two days a week off and put me in his spot firing for Russ Fischer two days a week (I was the regular brakeman the other five days) and someone else took my Brakie slot. This lasted about 2 1/2 weeks until one days at Osier all of us had a melt down at the same time and started yelling at each other. Weirdly, all of us independently went in and asked to lay off a couple of days. Shortly thereafter we started getting regular days off.