Just guessing:

I think the sight blade and operating button may be machined as one piece. The screw thru the operating button could be used as a sight adjustment for a different impacting load. The screw could have a concave end to ride on the ball in the base (if that is what it is?)
Is it possible the blade/button assembly is held in the open/closed positions by a flat spring that operates off a notch in the blade/button assembly?
This would negate the need for ball detents.
As far as assembly, I can only guess the main pivot pin is a press fit???

Dodging lions and wasting time.....