Ted,
I remember when the 51/191/31/14 came to the CRRM. It was part of the continuing Bob Richardson "Great" series. This was the "Great Locomotive Swap".
When the locomotive arrived, the frame of the locomotive was found to be broken (remember this thing had set for a LOOOOONG time in very humid conditions). The frame of the tender had reverted to its "elemental composition" (aka dust) while on display in Rhinelander. The tender tank had been modified and was beyond restoration. The hatch had been removed a long time before. The tank had acted as a cistern and the only thing that was holding the rust together was the paint that was left. Where the rivet lines were, there was a bit of corner metal remaining but nothing to bite on to.
The tender flare had been torched off sometime in the past (no, it wasn't by the C&S... the locomotive was sold before the C&S made those modifications). It was replaced by a piece of lumber sawn in the shape of the flare and painted black.
The decision was apparently made to rebuild the tender frame (which was done) using the salvagable original parts (it was not a new or wrong tender).
The tank, deemed beyond salvation, was condemned and removed. The tank was replaced by a D&RG replacement tank found in the San Luis Valley and moved to Golden for just that purpose.
Before you cry "Foul" I must remind you that the tank on the 51 probably wasn't original either. Tanks had a very short life span and replacement tanks were purchased and replaced as a matter of course. On the replacement tank, the name of the replacement tank manufacturer was noted (although the name escapes me now). This tank, although numbered for a C-16, was a purchased by the D&RG as a replacement tank, it was not original to any C-16 as purchased.
Hope this helps explain some of the sites breif explanation.
Rick