triva questions

Some Saturday ramblings,
Can anyone chart the number of operable Rio Grande NG engines for any given year over the last half century? Or the number of miles they operated?
If so, how does the "tourist years", say post 1967, compare to the say the 50s or early and mid 60s?. Do we have more locomotives operable today than in say 1962? Or does the cumulative miles traveled this year exceed those in 62? (1962 just thrown out as an example year).
I'm just curious if there is an objective standard that we can measure activity. We all know that indeed the trackage is much reduced since 1950, but there are other measures to be looked at.
Employment would be yet another measure.
Is there any other class of locos better preserved, anywhere in the world, as an operable class than the K-36? Not many have seen the scrappers torch, many are operating, others at standby, or preserved for eventual operation.