Originally Posted by
UKtravelbear
There must be some exemptions as otherwise lots of people would be missing their baggage for ever if bags weren't allowed to travel on other flights because they wern't loaded onto their international flights to the US in the first place - they get additional screening by both security on departure and customs on arrival.
Thousands of bags go missing on international flights every day and are later reunited with their owners. They transit multiple borders without issue. However, they do undergo additional screening and the separation is involuntary. E.g., the passenger neither causes the bag not to be loaded nor knows of it prior to boarding his flight.