Kudos to archivist Trevor Plante, who grew suspicious of the date as written and brought it to the attention of the NARA inspector general, and to the investigative archivists who followed up on the hunch and interviewed Lowry. During the course of that conversation, Lowry admitted having brought a pen into the archives and altering the date.
In an interview with the NYTimes, Lowry denied making the alteration.
Unfortunately the statute of limitations on this crime has expired, so Lowry can't be prosecuted, but he's been banned from NARA facilities, and I certainly hope other research institutions will follow suit. There's a special place in hell for people who do things like this.