How long is a piece of string?
Determining the length of a race course is by no means as simple as I thought and some research by Curtin Uni in Australia http://www.cage.curtin.edu.au/~gordonsj/course/
is interesting to read.
It has always been a contentious issue for runners, cyclists, motorcyclists or anyone who races on the roads.
My opinion is that the winner is the fastest person to reach the finish line and the distance, while academic, matters little except for those statistically inclined.
Unfortunately we will never know the exact distance of the original Mountain Course as there is no accurate data available.
It would seem to me as far as changes to the actual course affects times, it would be the radius of the bends, the road crown camber, the surface material, smoothness and levelling of humps, that would be very important at the TT over the years.
This ignores the development of the racing machinery.
Perhaps riders who have raced over a number of years would know if there has been any change in the lines of sight around the course. I have seen old pictures where there seem to be less trees in some areas, Ramsey hairpin for instance.