I won't admit to being "smarter" but here is my take on your cabinet.
First pic; the arched piece with the missing bolt should be pushed forward and I'll bet there is a matching hole in the frame piece just inboard of the drawers.
Second pic; the metal button in the lid mates to the metal insert on the cabinet top to prevent wear when the wood contacts wood.
The hole is for a vertical support rod to help hold the lid up when you put weight on it. Therefore preventing pulling the hinge screws out.
Anyway, that's my theory.
Joe