Other signal will be fused in. Otherwise, you’re counting on the possession of your government credentials as the control. You could just as easily swap IDs.
Leakage is expected, leading to iteration on edge cases. Some leakage will always be inevitable, no system is perfect.
The legal system is the final recourse mechanism if malicious activity (identity fraud) is detected.
Currently you need to look kind of close and have the other person's ID. With the 1:many pilot it would just check your face against a database of ID photos of PreCheck enrolled travelers, so you only have to be at the right place at the right time, and look very close. Not a huge concern in general, but for an evil twin it's much easier to get past TSA if they know which plane their twin will take.
Present state. They are moving towards facial recognition with no need for ID presentation or boarding pass. No need for the ID when they have your photo on file (this is how Global Entry re-entry kiosk works), and your identity is tied to airline PNR.
Leakage is expected, leading to iteration on edge cases. Some leakage will always be inevitable, no system is perfect.
The legal system is the final recourse mechanism if malicious activity (identity fraud) is detected.