"So I wasn't "worried", but wanted to avoid the hassle of post-flight-credit, and I am still amazed that this was such a novel concept to JL. "

im not too surprised. I had similar difficulties a while back with TWA ( after they had been taken over by AA ). I made a booking on an AA codeshare on a TWA flight. On the day of departure I changed to an earlier flight and insisted to the check in agent that I be booked on the AA number in order to get mileage credit to QF. The agents in a v blase manner insisted that there was no issue with mileage credit regardless of the flight number ( despite my telling them that Qf was not a partner with TWA ). Despite my insisting on an AA number, the agent took the easy option and booked me on TW. Fortunately QF did give me credit when I explained the situation

Dave