I think you're correct in the most technical sense. However in a very practical sense the world of Dynamic soaring is very close-knit society and culture, and the names of th "Big Dogs" are known just as everone here knows of QuiQue Somenzini, Andrew Jesky, Chip Hyde, etc.. To gather "the correct" officials to verify the speed as an "official" world record would not be possible given the time, locale and opportunistic nature of this activity.

A very comprehensive web site is maintained (daily) to track the goings on in the DS world:

http://rcspeeds.com/

And this web site is well known and utilized "world wide" as "the authoritative" list. All it really takes to document one's speed is to have a person willing to hold a radar gun at a plane and "witness" the highest reading which most modern guns will automatically do.