Those tests are “red team” exercises, they are designed to exploit weaknesses in detection such as using X-ray proof bags and 3D printed firearms. The whole point of these exercises is to show they can happen so security posture can improve.

If the red team got caught (the 20%) it’s worth noting because those were “noisy” after the more quiet tests were completed. The red team conduct these to get caught to have a baseline on where the posture is at.

Source: this is my job in private sector