The body was assembled around the floor in Single Body Units. i.e. Panel, Suburban, Canopy Express. Replacing the rear floor in a Single Body Unit is not a easy task. Panel truck Factory Assembly line. Photo one Photo two
So the Panel Truck and Canopy Express got the one-piece floor in 1950, but there is no mention of the Suburban getting it that year. So perhaps the respective body styles DID get them in different years?
From the pics you posted the bodies REALLY WERE built around the floors! I suspect few of us would go to that level of disassembly to install a floor the way the factory did it.