"Steam Cleaning" was invented in the mid 1960's. Portables only.
As I recall, Bill Bane came up with the idea of a high powered portable, run off electricity that would stay in the truck, and just hoses into the house, some time in the early 1970's.
That spurred several people to make a more powerful machine, some with a separate engine- called a "Slide-In" and some with the idea of the truck's engine making the power, and a drive shaft to the machine. This was in the early 1970's, and the idea caught on pretty fast.
In 1976, I saw at a convention in Las Vegas at Caesar's Palace, there were some 20 manufacturers of Truck Mounts displaying, so the idea spread pretty fast.
Very little has changed or improved since then.
But in the 1950's? I was there- it did not happen. I never heard of a "Pringle" at any time.
Gary