Whenever you check a bag and declare a firearm you and the airline representative go straight to a TSA checkpoint for the hand off. I'd be willing to bet it was 2 instances of idiots not properly securing and casing their weapons, and then checking them, or just throwing them in their checked baggage thinking that's all they needed to do.

Also I'm about 99% positive all checked baggage is X-ray inspected before going out to the plane, some airports still have the machines out in the check in area and you hand it off to a TSA representative and they put it through the machine before it goes on the belt to baggage handling.