Monarch Pass

Sort of another bit of the "I wonder what surveys survive" thing from earlier in the year. During 1880 D&RG surveyed both Marshall and Monarch passes looking for a route to Gunnison. Both were found to be similar in grades, curvature and estimated construction cost. Marshall was chosen because the toll road Otto Mears had built gave better access for grading and bridging crews, speeeding the work.
Here's the question: If Monarch pass could be crossed with a line at 4% by the 1880 survey, why did the Monarch branch wind up with grades up to 4.5% and a switchback in 1883? Had they lost the 1880 survey? Were they being penny wise and pound foolish by using a cheaper route for construction which imposed higher opertaing cost evermore?
Inquiring minds want to know.

hank