"Rocky Mountain Views" was changed a number of times over the three-plus decades it was produced. Not only did the locations change, but some scenes were re-photographed to show newer trains. The best example is the classic Royal Gorge shot on Hanging Bridge which usually featured on the cover; I've seen it with small power, and with later large power.
If I understand it correctly, the main sales point for the book was on the trains, so D&RG(W) had some incentive for keeping the pictures current. Also, in some (probably later) editions, the captions were moved from a grouping in the front of the book to face the photos on each page.
JAC