I've done 2 triathlons organised by concept sport and both were supposed to have 400m swim, not a problem easy enough to measure yourself in the pool. One had a 14 mile bike section the other had 15 and the runs both supposed to have had 5 miles runs to finish. I know from my own road races that the 5 miles must have been short on both course as my times were 27 mins and I've not run that time for 5 miles on a road race nevermind after 2 other disciplines.
So how do we know if the courses we do are accurately measured? It seems to be the runs more than the bikes as I drove round the bike sections and they were about right.