Couple of points. Note the photo of the gun with "Patent" around the thumb lever. Every gun I have seen so marked was a
Screw Grip, but not every Screw Grip was so marked. May have to do with production vs patent dates.

Second, I don't believe W&S used the Screw Grip action for best work guns. The top of the Screw Grip line was a very nice gun, indeed, but not quite a best work.