A 12-gauge, 30-inch, choked modified and full was the norm for North American doubles from the 1890s to WW-II. Virtually anything else was a "specialty" item. Used for everything from Quail to Ducks to Deer. The vast majority of shooters/hunters only had one shotgun and if it was a double, that was it.
For example, Fox made about 107,000 Sterlingworths in 12ga compared to 45,000 16 and 20ga Sterlys, combined.
Your point is right Larry, but two and a half decades of recording Sterlingworth serial numbers shows nearly 20000 less total. There is a 16000+ gap in the 12-gauge serial numbers from the high 143xxx range to 160000, and in the 20-gauge Sterlingworths a 3000+ gap from the 266xxx range to 270000.
There may be some other gaps too, as Savage seems to have blocked serial numbers. Examples -- all the guns recorded to date in the 134xxx range are Fox-Sterlingworth Wildfowls and all from 134102 to 134130 with no other 134xxx serial number guns recorded. Guns recorded in the 135xxx range are all Fox-Sterlingworth Skeet & Upland Game guns and are all in the 1356xx and 1357xx range with no other 135xxx range guns recorded.