Remember that logging flighttime as you describe is perfectly legal in the US which is an ICAO member so it can't be denied by any other ICAO state, so log it! When it comes to a company, it is of course a different deal. But by the time you get to HKG it would nost likely be a very minor portion of your flight experience and you did nothing wrong, just be aware that they might decide to not count those hours. use it to build time for your first job in the US, then fly and build time for CX.
I stand to be corrected