First, TSA employees themselves will have higher exposures than fliers, so any resulting health problems should show up in them soonest. (Even if doses are low, as some have pointed out the machines could have glitches due to a variety of factors. Will glitches causing transient high energy levels be caught?)
Further, there will be measurements, one way or the other. Radiation badges are easy to get, are small and easy to hide. It’s not hard to envision scenarios where formal and informal radiation studies will be underway, in the very near future.