Well, yeah, because in 1950, Archer H. Shaw released the Lincoln Encyclopedia, which purported to be a one-stop shop for all things Lincoln. The problem is that he didn't do his due diligence in terms of authenticating things he put in the encyclopedia. He includes the letter that this quote comes from in that encyclopedia, a letter supposedly to Colonel William F. Elkins, but historians and researchers have clearly determined that that letter was a forgery. Far from the only example of the lack of completionism in his book, and thus it's not seen as a well-put-together resource for information.