On page 192 of Dorman's _Rio_Grande_Southern_An_Ultimate_Picture_ Study_ there is a page from a train register from Dolores of February 24, 1926. It shows Extra 361 East, light, out of Dolores for Rico about an hour aheard of Train 382.
From our research in the old and largely defunct Rio Grande Southern Historical and Technical Society, Gabe Bradford and I believe that the C-21's were used quite a bit during the '20s.