Greg, that's a good question and from what "little" I remember of 'commercial' models , back then (before my time too!)the only difference was the military models had the "H" and then the "H" and a "P" , the commercials did NOT. as those were military acceptance stamps. Later for the 1911A1, the difference was a "G" for the military models and an "S" for the 'commercial' and again , they added a "P".
I know that Chuck (Mr. Clawson) showed all the "military markings" for all the 'service guns in his books, to differentiate from the different "vendors" (contractors)
Most all the early .45's I have ever owned were of the military type and had the "H" and then the "P" added later on. The "H" was in different 'positions' on the barrel also,either on the end of the barrel hood, and later moved to the top of the barrel.
As well known, this "H" was for Frank Hosmer, the principal Ordinace inspector. Later ,just before WW II, another inspector with the name of Hauft or Haump or such used the letter "H". Frank Hosmer was from 1911 until 1925.