This came up reading the thread about the Quad Cities Marathon (see article at end). The lead runners were led off course by the lead biker, and as a result they ran the wrong course and were disqualified. Like many road races, I imagine this one had a condition that "runners are responsible for knowing the course", and so this ruling was probably correct by the book.
But I hope we can agree that in practice, it's actually NOT the runner's responsibility to know the course. Races have markings and volunteers, and other competitors to follow, and with any reasonably large race, there is an expectation that these factors are enough to keep the runners on course. Again, this isn't a value statement: in most races, if everyone had to run the course alone with no help (never mind a volunteer giving incorrect directions), the vast majority would get it wrong somewhere. The race and race prep would be completely different. Everyone would be running on the course days before the race, cramming the night before, and strategically running with a group through tricky sections. We DON'T expect this as a normal part of road racing, so in practice we DON'T consider it the runner's responsibility to know the course. (Trail races are completely different in this way).
Instead, the only time this rule comes up is when the race organizers mess up, either by a volunteer pointing the wrong way or the course being insufficiently or improperly marked. In this case, the race's response is always "well, it's too bad, but as we all know, it's not our responsibility."
There's an expectation that is put forward and encouraged by the race (that the course is well-marked and well-directed), and this expectation is important to the customers (many fewer people would sign up for the race if they expected to be led off course), but it is not legally guaranteed by the terms of the contract you sign. So the race benefits from the expectation of a service, but doesn't suffer from a failure to satisfy it.
I think this expectation should be codified in some way. If a road race wants to be sanctioned at a certain level, they need to take responsibility for course markings and volunteers knowing the course. Otherwise, they're liable to pay out double prize money when applicable if their mistake affects the race. If a race REALLY expects runners to know the course (instead of just saying that to avoid liability), then they should make clear that they're a different sort of race.
https://www.washingtonpost.com/nation/2021/09/28/man-wins-quadcities-marathon-runners-mishap/