What do the immigration people do with those that arrive on stolen passports? Can they return them? Where to? If the "refugees" don't cooperate, immigration will never know where they're from, thus can't ship them back.
I can confirm that if a passenger presents themselves at immigration having "forgotten" where they boarded the aircraft then the immigration can ,and do, look at the CCTV footage between the aircraft and gates to work out which aircraft they arrived on. once this has been done removal directions are issued and the passenger goes back to whence they came at the cost of the airline. it is not fool proof but it does work