I'm sorry if this is a silly question.

I own a 4 screw pre 29. How is this possible?

As I understand it, Smith went to model numbers in/around 1957. I also thought that the 5th screw was eliminated in 1959. While I totally understand sometime old parts are slow to be used up, in this case it would seem the reverse would be true; ie any 4 screw would have been built AFTER model numbers were implemented.

Am I missing or misunderstanding something? Or, are my dates wrong?

Just curious, regardless I really love the gun!