I don't think that the #4 was an actual thought when the knife pictured was made. The Commandos were early Hunter style blades with a sharpened top bevel. Some Commandos were "one off" blades. The WWII Hunter was the precursor to both the post war model 3 and model 4.

The WWII blade grinds varied in the Hunter model and you could probably make an argument that one blade looks more like a model 3 and another looks more like a model 4. Hence the "3 1/2" term coined by Pete Hamilton.