Though Hofzinser invented the double-backed card 150 years ago, it remained otherwise unknown to magicians until Theodore DeLand used it in two tricks, "The Two-Card Monte" in 1913, and "Inverto" in 1914.
These are, I believe, the first recorded instances of anyone in the United States publishing or marketing a trick with a double-backed card. It is unlikely that Vernon would have heard of the double-backed card were it not for DeLand's marketed tricks.
I have several versions of "The Trick that Fooled Houdini" from Larry Jennings for the upcoming books. And, should the mention of those books simply bring a chuckle to your lips, it might be of interest to know that Noah Levine is now proofreading "Mr. Jennings Takes it Easy!"