Would Lichtman's Keys model failing be unprecedented?

Lichtman's Keys failed in 2016 - note that his model does not predict the Electoral College winner, but the winner of the popular vote. From the man himself, in the introduction to his book Predicting the Next President - The Keys to the White House 2016:

The keys to the White House focus on national concerns such as economic performance, policy initiatives, social unrest, presidential scandal, and successes and failures in foreign affairs. Thus, they predict only the national popular vote and not the vote within individual states.

_{Introduction - Page 4}

In September 2016, the Washington Post published an interview with Lichtman, where he reported that his model narrowly predicted a Donald Trump win:

So very, very narrowly, the keys point to a Trump victory. But I would say, more to the point, they point to a generic Republican victory, because I believe that given the unprecedented nature of the Trump candidacy and Trump himself, he could defy all odds and lose even though the verdict of history is in his favor. So this would also suggest, you know, the possibility this election could go either way. Nobody should be complacent, no matter who you're for, you gotta get out and vote.

Although Trump went on to win the electoral college, he did not win the popular vote, marking an end to the keys' record for successful predictions. According, again, to Lichtman's book, the keys have otherwise successfully predicted the popular vote in every election since 1860.

The keys that anticipate the outcome of the popular vote in every election since 1860 close the chasm opened by conventional political commentary between the selection of a president and the governing of the country.

_{Chapter 13 - Lessons of the Keys: Toward a New Presidential Politics}