That seems statistically likely.

There's a fair amount of math and industrial job design/psychology you could use to analyze it. But the logic you laid out gets to a big part of the problem. Given a relatively constant inspection time, the greater the number and variety of items you look for, the greater the likelihood that at least one of those prohibited items will pass thru undetected.

In plain language, it's a choice between doing a few jobs well and large number of jobs poorly.

Toss into that the mind-numbing randomness and number of truly trivial changes.

The result is a flawed process which -- even if perfect -- is almost certainly to be misapplied by under skilled, undertrained, undermotivated and understaffed personnel.

Which just reinforces what I have said before: The TSA is a political solution, not a security solution.