In my 1914 catalog they are simply described as "Proprietary", my 1933 catalog shows "Model 400 Proprietary Hammerless" and "Model 500 Light Game Model". The primary difference seems to be the Model 500 has 25" or 26 1/2" barrels compared to the 28" or 30" barrels of the Model 400. Also, the Model 500 is shown as a single grade (Grade 2) rather than the three grades available for the Model 400.
I must say, this is one of the reasons I find these guns interesting. The variations produced seem apparently limitless, subject only to the whims of the customer.