FWIW, their final poll was Clinton +4, with a +-2% accuracy, and the final vote was Clinton +2, so they were pretty close, within their margin.
What happens with some of these polls is that the final ones are nothing like the ones when the election is a few weeks away. When they rate poll accuracy after each election, it’s based only on the final poll. Common sense tells you that a 10 point change is highly unlikely in a span of a few weeks. What happens is the final ones are at most just slightly manipulated, unlike the earlier ones that were essentially fabricated.