The case colors look good and could easily be original. Screws that have bluing on the frame wouldn't wear any more than the frame, as a holster wouldn't touch the screws anyway.
Here's the thing. The screws protrude higher than the frame, and the case colors are worn off. So you have an area where there is no case coloring left, and then a very lighly worn screw right next to it. So how did the case hardening go away without the screws being affected? The other screws match the patina of the rest of the gun, but these don't. Also, all the other screws show deformation marks from being assembled and disassembled, yet those 3 screws have screw slots that are perfect.
The screws are originally Nitre blued, which is notorious for not holding up well. So if the case colors are faded, worn, etc., it just makes sense the screws would have worn also. If they were recessed into the frame and below the area that's missing the case colors, then your statement would make sense. But you can clearly see from the photos that the screws project beyond the frame on either side.
