It's all so mind-numbingly ridiculous.
On one hand, the TSA wants to put on this face to the public that they're this organization that wants to eliminate every single possibility of something passing by the checkpoint.
Yet the people being paid to seek out such prohibited items, whether it's on a person or in a bag get multiple chances to make up for their errors (including GAO tests).
Does the TSA realize you don't get "do-overs" or "remedial testing" in real-life?