McSorley's Ale House is not 149 years old. It opened in 1862.
See the New York Times, Sunday November 19, 1995 Streetscapes, and Sunday September 29, 1996 The City section. The American Institute of Architects (AIA) Guide to New York City, latest edition, 2000. The Blue Guide to New York City, W.W. Norton, 3rd Ed. 2002. NEW YORK An Architectural Guide To The Metropolis, McGraw Hill, 2003.

I much prefer the quote from the New York Times on August 27, 1997

“Like many an old barfly, he didn't plan on ending up like this, but hard times drove him there. The $700 that bar owners pay him to dig out the history of their buildings helps McDermott cover the costs of his real passion. . . “

The Times refrains from calling McDermott a shakedown artist, but you get the idea.

McSorley’s should pay him the $700.then he will admit what the rest of the world knows - McSorley’s opened in 1854.

Who is Richard McDermott, and more importantly: why is he such a wanker?

McSorley's has been written about since the turn of the last century, and it always used, even then the 1854 origination date. In a 1913 Harper's article, same date of 1854. It makes absolutely no sense that the owner then (I think it was Bill McSorley) made up the date. Hell, how would he know the place would survive into the 21st Century? Besides, records often conflicted back then. I saw a copy in the bar showing the ship manifest from 1851 when John McSorley entered the U.S., fleeing the famine.
Hell, there are guys out there claiming that the Holocaust never happened, too.