Deep Sea Loot is listed on the back of the 1922 Boys Cinema Card. Chief among his films are: “The Master Mystery”, “The Grim Game”, “Deep Sea Loot” and “Terror Island”. Notice that Deep Sea Loot appears after The Grim Game that was released in 1919 and before Terror Island which was released in 1920.
According to Picture Play Magazine [Mar-Aug 1921], some of his pictures are “The Master Mystery,” “The Grim Game,” “The Deep-Sea Loot,” and “The Adventures of Houdini in Paris.”
According to The Lincoln Star [Sun Aug 20 1922], he has made several pictures before “The Man From Beyond,” among them are “The Master Mystery,” “The Grim Game,” “Deep Sea Loot,” “Terror Island,” and Adventures of Houdini in Paris”.
And Deep Sea Loot for Famous Players Lasky Corp, 1919 was included in Houdini’s typewritten list of screen credits.
But, according to Disappearing Tricks by Matthew Solomon, during the 1910s  Houdini worked with underwater filmmakers J.E. and Ernest Williamson on a never-completed film (prospectively titled Houdini and the Miracle) that promised to show Houdini’s escape from a photosphere (an observation chamber that housed a camera that was attached to the bottom of a barge by a long tube).
According to ” a full page ad in The Moving Picture World on May 5, 1917, “Houdini’s Sub-Sea Miracle” was supposed to be released in November 1917 as the Williamson Brothers second film of that year.
Solomon also mentions that the Houdini and the Miracle  film project was included in Houdini’s typewritten list of screen credits as Deep Sea Loot  but was never made [completed].
What intrigued me was the 1917 date versus a 1919 date, the Williamson Brothers versus Famous Players Lasky Corp and the following 1919 Houdini letter from the Fred Pittella collection:
Nov 2 1919
Dear G Kirby
We are on location and expect to return to Los Ang end of week.
I am doing under water swimming getting ready for my “Deep Sea Loot” story.
This morning I did five tests each running over two minutes which is not bad at this stage as it means 3 minutes next week.
So, in November of 1919, it is my understanding that Houdini was at Catalina Island working on submarine scenes for Terror Island [Deep Sea Loot?]. [Wid’s Daily Dec 1, 1919]
In December, the players were transferred from Catalina Island to an island off the coast of Lower California. At this island, which has a South Sea atmosphere practically all of the remaining exterior scenes were filmed. [Motion Picture News Dec 6 1919]
According to Kalush p 354 and 355:
By July of 1917, three months after signing a contract, Houdini was still hashing out the script with the Williamsons. Both the war in Europe and a war between the Williamsons derailed the project. Desperately trying to salvage his film, Houdini entered into an arrangement with a company called Westart to film the opening scenes of his scenario, a manacled jump into the sea off the pier at Atlantic City. Though Westart would in a few years produce a series of low-budget Westerns, this one-day shoot appears to be all that became of The Marvelous Adventures of Houdini.
According to Solomon’s notes:
Elements of this story [“The Marvelous Adventures of Houdini, the Justly Celebrated Elusive American”, aka “Houdini and the Miracle”], especially its focus on underwater action [“Deep Sea Loot”], found their way into “Terror Island” a few years later.
So in 1919, did Harry Houdini shoot scenes for “Deep Sea Loot” and “Terror Island” or are they one in the same?
Special Thank You to Fred Pittella for allowing me to share the contents of a letter dated Nov 2, 1919 from his personal collection.