Mike, I have not heard of the "Course Measurement Working Party". Are they well-represented in Parliament?
Guidos, I don't look at this as a problem begging for a solution, rather the discussion is to make measurers aware of the differences in measurements on paved vs. non-paved surfaces.
If calibrated on pavement, a measurement on non-paved surfaces will be longer than our click-counts would indicate. If we are interested in not only assuring that a course is "at least as long as advertised", but also assuring that the course is accurately measured, then we need to be aware of the variance.
Unlike you, we have plenty of gravel-road courses out here in the unsettled west. I have not had to measure one in the last two years, but prior to that I did 5 or 6 half-marathons and marathons on gravel. In hind-sight, they are all likely to be way over our SCPF long. Based on comparisons I did two years ago (concrete vs cinder trail), the Half courses could be 200 yards long, or worse, and Marathons even longer. I don't want courses to be long just because they are on gravel.
I would suggest that people calibrate on the dominant surface of the course. If I do any more gravel courses, I will tape out a calibration course on the gravel (or cinder rails-to-trails) surface, and not rely on an asphalt calibration. Just interested in accuracy of measurement, not just going through the motions of calibration, measurement, and having the course longer than our SCPF.