After the discontinuance of the Chili Line and the Shavano, 3 K-28's were sufficient to protect service on the San Juan. The Silverton Branch was not yet hauling tourists and there were K-27's available for the mixed train there. Unlike the K-28's, the K-27's could pull double duty--on the Silverton Branch and on lease to the Rio Grande Southern. The K-28's were too heavy for the RGS trackage.
Also, 474 was not usually assigned to passenger service--it was generally used on the Crested Butte Branch. If you note in the photo posted elsehwere, it had a yard pilot--handy for switching use in Crested Butte. I was told it did not have a steam line running through its tender, so it could not be used for winter passenger service.
One also has to remember that, during WW II, the drilling boom had not started in the San Juan Basin. Traffic on the San Juan Extension was not that heavy. Most of the K-37's were assigned to Salida for use over Marshall Pass and on the Monarch Branch, both of which were busy during the war years. The K-37's were swapped for a number of K-36's for Marshall and Monarch service not long before the Valley Line was abandoned. It is interesting to note that of all of the active K-36's today, all except 484 and 488 spent a fair chunk of the 1950's working out of Salida. (487 was also in Salida, but was a relatively early "returnee" to Alamosa.)485 was scrapped in Salida, after it "slept-walked" into the Salida turntable pit. Many of its parts were used to rebuild 489, the last locomotive overhauled in Salida.
K-27's, 28's, 36's, and 37's--I love 'em all.