There are some extractors on two hook and early large hook guns that are not retained with a screw as in the later guns. If pulled hard enough, they can come right out. they are held in by tension from a small spring inside the barrel lug.
Now... there is even some variations of this design. I have observed guns as close as 50 numbers that had different extractor operations and retention designs.
A Pain... I know.

B.Dudley