Despite extensive ground testing, NASA got very lucky with the Saturn V.
The second flight of the rocket, SA-502 (Apollo 6) experienced extremely violent pogo in its first stage that nearly caused the loss of the vehicle and did damage the upper stages. The second stage had other problems including an early engine shut-down and electrical shorts which meant it couldn’t be restarted. Had they occurred on a manned flight, the abort system would almost certainly have been triggered.
