That is correct, there was no dual gauge around Ridgway - One day it was narrow, next day it was standard! But the idler cars were often used by crews using narrow gauge engines to switch the dual gauge yards at Montrose and Salida and they used the idler cars for this service. Most idler car action was yard switching. The Alamosa - Antonito and Alamosa - Hooper line haul use was the exception, rather than the rule.
As with many "standard practices" we hear reported, this was the final useage that most of us living got to see, and we tend to think this was the norm.