I believe only the target sighted models are properly called "Mk I"'s. The fixed sight tapered barrel guns were simply called "Standard Automatic". Since there hadn't been any changes planned in the beginning, there was no need for a "Mark" number. The adjustable sights were the first change. Most people however refer to anything pre Mark II as a Mark I.
That would appear to be correct according to Fjestad's Blue book. They list First the Red Eagle Standard and Target Model. Then the Black Eagle Standard Model, then Black or Silver Eagle Mark I target, Mark II Standard, Mark II Aniversary, Mark II Target etc.
It says that the original Red Eagle was changed to a Black Eagle in 1952, in memory of the death of Alexander Sturm who died in Nov 1951.