Since the yoke's assembly number does not match the frame's 5883X the yoke was replaced. Based on that here's one last guess. Something bad happened to the original yoke. Maybe it was lost. Maybe its tube was bent and the owner did not have the tools or know how to straighten it. S&W yokes, side plates and cylinders are not intended to be drop in parts, not even between revolvers with consecutive serial numbers. Perhaps the file strokes were enough to make a replacement yoke drop in and the dash 4 was over stamped. The dash 4 looks almost the same but it is taller than the 4 in the Model number. That's my best guess.

Regardless, it is only a cosmetic issue in a spot that does not show. I'll bet it is one of the easier snub noses to shoot accurately.