Jasper Mocke during record Miller's Run - photo from video
Some record holders mentioned in these lists may have been participating in multi-boat races when they set their records, but for the most part these records are created and improved on by single boats. Levels of support from helpers or support teams may have ranged from zero to significant. Levels of precision in time-keeping, exactness of course, etc. range from very precise to very informal.
(Typically just recorded or observed by participants - all in good faith)