It may be that this concept of regulating screws came from the cartridge era of double guns from Europe, and America. In this case, where steel is fitted to steel, such as the trigger plate into the receiver, it is a simple process to regulate the slot of the screw, as steel on steel changes little over time. Likewise, the butt plate rarely if ever is removed, so those two screws having aligned slots is also no issue. But on a longrifle - I doubt it was a consideration.
