The rather obvious statistically implied probability we can infer from the number of accidentally packed guns that were detected is that a record number of accidentally packed guns also passed undetected through TSA checkpoints and safely flew on airplanes to their destinations.
Article says the most common reason given was that the person forgot the gun was in their carry-on.
That seems strange, I guess if you are doing a short hop and you just grab your backpack I could see forgetting, but I'd think most people intentionally pack a bag to take aboard a plane.