Those experts that have studied the syntax, the construction and phrasing of the sentences, have concluded that the entire Beale Papers story was created by one single author, including the "letters" that Beale sent to Morriss on which the entire treasure story is based.
While the various influences that were utilized to create the adventure and treasure portion of the narrative text have been discussed, it is apparent that this "unknown author" had additional impute from those around him.
As the perilous adventure and treasure portion on the story shows a masculine hand, the description of Morriss and absolutely that of Beale show a very feminine hand, the quintessential tall, dark, and handsome stranger.
"In person he was about six feet in height, with jet black eyes and hair the same color...he was a model of manly beauty favored by the ladies and envied by men...he was reverentially tender and polite".
One author's syntax is obvious in the manuscripts construction, but several different minds were involved in the creation of the story.