I'm pretty sure the average tourist who is required to pay a full fare if the C&TS is to ever be at 'break-even' financial conditions doesn't care at all about historical accuracy -- they just wanna' be occupied and entertained.
As far as Osier (circa 1881?) itself, anytime from early 1880's to late 20th century reenactors would seem to be ok. Considering the location and overall history of the D&RG and the San Juan's, I think it would be ok to tell stories (historical or fictional) from the pre-Spanish era through the Atomic Age. All periods are relevant to some degree, and if they entertain the average tourist then they were worth the price of admission.
Tom