In the last month, I was reading another bulletin board that was having this same discussion. If I had time to look for it I would, but I am short of time right now.
But, there were a couple posters who claim to be inside the triathlon governing body, and they claim that the rules state that a distance must only be within 10% of the claimed distance. They acknowledged that a "marathon" course in a triathlon could be 38km (instead of 42.195 km) and still be considered valid.
To us in the running community, that is misleading. But, those are apparently the rules, as the triathlon community apparently feels they are competing against other people, not the clock. Thus, the organizers don't see a need for accuracy in course length.
Just sharing what I read recently.