It's important to note that the "bags" are only exempt from legal search and seizure at e.g. customs or by police. If they're not equipped with effective tamper

It's important to note that the "bags" are only exempt from legal search and seizure at e.g. customs or by police. If they're not equipped with effective tamper-evident seals and/or escorted by a trustworthy courier at all times then they can (and probably will) be intercepted. It's tough to gain access to the small ones, but a shipping container is much harder to keep under watch at all times. It only matters if you get caught with your hands in the cookie jar after all. I'd guess the typewriters weren't shipped in tamper-proof containers and were simply altered en route. I once read a story that I can't find again about the CIA intercepting a shipment of (what I think were fighter planes?) and disassembling them overnight, then putting them back together to be on the train again the next morning. It was a great story, I wish I could find it again.