There is a lot of talk about overlap in variations and changes.  A lot of beginning collectors assume that everything was done strictly in order, which just didn't happen.  I believe parts were placed in a bin and removed when needed.  Date and machining changes were simply ignored.

In mid-1943 they changed the frame by machining it differently.  More steel was left around the trigger axle pin for reinforcement.  You can see that because of a downward "hump" that is in the frame where the pin goes through.

About the same time as the addition of the "hump", there was a change made to the machining of the slide.  On early slides there are two cuts where you see the extractor.  The second, smaller cut was eliminated so it is referred to as a "late" slide.

This is a later 1943 example that has an early frame without the trigger axle pin reinforement and early slide cuts.  This gun is about 3000 guns past the other byf43 that I have in the "f" block.  By looking at the two guns you can see how overlap occurred.

Click HERE to see an example of a slide with the late configuration extractor cut.