One should also note that by the Great Depression years of the 1930's, the D&RGW had a surplus of narrow-gauge power. The K-27's were mainly used on the lines (both D&RGW and RGS) where lighter rails and bridges precluded the use of heavier locomotives.
By the second half of the 1930's, even the K-28's, though excellent locomotives, saw their use pretty much confined to the remaining passenger trains (the San Juan and Shavano), the Chili Line, and--less frequently--on the Silverton Branch. 474 was the exception--used almost exclusively on the Crested Butte Branch.
When the call came from the War Dept. in 1942, the D&RGW deemed 7 of the K-28's surplus--the Chili Line and the Shavano were gone--and they felt that the remaining 3 K-28's could protect passenger service on the San Juan. Thus, the K-27's were left to protect service on the Silverton Branch, and on the shriveling network of "light" lines of the D&RGW and RGS, while the K-36's and K-37's protected freight service on the San Juan and Gunnison extensions.
By the early 1950's, the RGS was gone, as was the western portion of the Gunnison extension--and the K-27's protecting that service were scrapped. 453, 463, and 464 were held for switching service in Durango and/or service on the Silverton Branch. When the D&RGW deemed that the K-28's were sufficient to protect the Silverton Branch, the remaining K-27's were set aside, with the 453 being scrapped, the 463 sold to Gene Autry, and the 464 left to sit derelict in the Durango yard. In the days before the D&RGW was denied permission to abandon the Silverton Branch (that occurring in 1961), both 473 and 478 were reduced at times to the role of yard switchers (being equipped with yard pilots) and as backup engines on the Silverton. I firmly suspect that, if the D&RGW's experiment with the US Army diesel switchers in the mid-1950's had been successful in Durango, both 473 and 478 would have likely been scrapped.
The latter day (and soon to repeat) experience of the C&TS with the 463 indicates that the superheated K-27's were, in fact, pretty darned good locomotives. The reason that all of them were not superheated is, as others have stated, simply a matter that the D&RGW had neither the need for them nor the money to upgrade them. It's a pity that the 7 K-28's are gone, but there is no question that they were economically surplus to the D&RGW in 1942 and the need for them in Alaska was real. No queston that the K-28's were (and are) dandy locomotives.
It is a miracle that examples of the K-27, K-28, and K-36 classes remain in service today. I would hope that a surviving K-37--most likely the 492--will be restored to operation so that all 4 of the "newest" remaining classes of D&RGW narrow gauge locomotives will be represented in the operating ranks of D&RGW engines. A running C-16 (223) and a running T-12 (169) would also be a neat long-term dream to come true, too.
