Today I played the fourth game of Covert Front "The Spark of Life" (Another game series made by Mateusz Skutnik) and I found many direct references of Submachine. For example, when the main character, Kara, is "teleported" to Von Toten's study room and she opens the door, she realizes she is in a kind of mover.
Another clue is when the figure of Karl Von Toten disappears, the only thing left is a red chair very similar to the one seen in Submachine 2: The Lighthouse.
And at the entrance of the laboratory we can see a force field, like in Submachine 7: The Core.
In the scene when the game ends, Von Toten is working on a device that it looks like the one found in Submachine 3: The Loop.
And after Kara and Karl escape from the Germans, in the background of the lab, we can see many machines that look like the ones seen in the Sanctuary in Submachine 7.
The most intriguing thing is the date where this game is set: 1904. And in that same year, the first modern Submachine has been created by an unknown group of scientists.
Very interesting, isn't it?