I have examined a number of D&RGW train registers from several locations and have also had a number of conversations with retired D&RGW crew men.
The pattern varies from location to location, but generally the helpers ran separate and as extras.
East bound freights on Marshall Pass normally had three engines and the two helpers would run light back to Sargents while the road engine would take the train onto Salida. In winter there would be a flanger between the lead helper and the road engine and the helper would take the flanger back to Sargents. West bound freights out of Salida would typically have a mid-train helper which would return to Salida from Marshall Pass. Sometimes after helping a west bound to Marshall, the helper would return to Poncha Junction where it might help a freight over Poncha Pass and then return to Salida.
On the Crested Butte branch, the Gunnison yard engine was often the mid-train helper and would return light ahead of the road engine.
Baldwin branch helpers would help with switching at Baldwin then run light back to Gunnison.
On the Monarch branch, the two engines would double the switch back and on the last down grade trip, the helper would run light to Salida ahead of the road engine.
On Cerro Hill, a helper would often come over from Montrose and three engines would take the train from Cimmaron to the Summit where they would do a "turn" if necessary. The Montrose helper would run light ahead of the road engine and the other helper would return to Gunnison.
The retired D&RGW engineer I knew once got demerits for running into the rear of the lead helper in the Cimmaron yards. He said the second helper would often chase the first down grade and it was a bit of a game to push the guy running ahead of you. That day, he pushed it too much and crashed into the engine ahead (I think he said he was running #318 as helper that day). He told the D&RGW officials that the brakes were not functioning well, but the reality was he was tail gating.
On the Silverton branch, if a helper was needed, it would run light back to Durango ahead of the road engine after helping with the switching at Silverton. Cumbres has been discussed in detail and the RGS too.
