ATC Watcher, the PNR message sent by the airlines don't reflect passenger transit airports, only departure and destination. There is no requirement for transit passengers to pass immigration control and have the passport inspected, hence they won't be logged. So, for example, a flight was routing SYD-DUB-LHR with pax A going SYD-DUB and pax B going SYD-LHR; the message to Dubai would only contain pax A and to the USA only pax B. Pax B as a transit pax would not go through passport control at DUB and their passport would not be scanned, hence no record.
The only way of the USA knowing would be to have access to hack access to all encrypted databases world-wide to see who was on all flights, be aware of the routes and transit points of all such flights and interpolate to infer who had transited through where.
Last edited by ORAC; 10th Feb 2016 at 09:05.
Reason: sp