Back in those days, typewriters had a single key for the number 1 and the lowercase l. But they did have the O and 0 as different keys.
It is possible that they saw the 4 floors as "representative" of all the floors that would be built, and just expected that there would be 40.
Wichita Falls is pretty much on the Texas/Oklahoma border and that area was filled with oil money at that time. Only 10 years later, Tulsa Oklahoma was building 40+ floor skyscrapers. But prior to that, skyscrapers seemed to be limited to NYC, Philadelphia and Chicago.