The D&S still operates with Timetable Authority, but uses a modified "Track Warrant" form as a substitute for the traditional train order/clearance card. With that said, an extra such as this would normally carry white flags (class lights at night only), but from what I have seen that didn't always happen historically. I lived in Durango throughout the 70's during DRGW operations and observed many work trains and never saw one displaying white flags, Sometimes you just forget and in the big scheme of things, this would be a pretty minor infraction.
My 2 cents