Re-export authority is what gives export controls extraterritorial reach. Items subject to the US Export Administration Regulations remain subject to them after they leave the United States, so shipping a controlled item from a third country to a restricted destination can require a US licence even though no US party is involved in that leg.
Diversion schemes are built on the assumption that the second leg will not be examined. Detection accordingly focuses on reconciling what a jurisdiction imports against what it plausibly consumes, and on the sudden appearance of intermediaries whose import volumes have no domestic explanation.