Interesting discussion. Maybe consider, in some cases, putting the distance in quotes if they want it there, the So and So "10 miler". Or maybe not. But if you can get away with just a no-distance name, I like Jim's solution.
I had the impression that a lot of those great traditional New England races had traditional lengths, usually short of the nominal distance. Maybe that's changed over the last 30 years.
Mark's suggestion allows us to keep in mind that there are limits to the accuracy we can claim.