aa.com (for what it's worth) is pretty clear that you are supposed to have access to Flagship Lounges at both ends:

At the new American Airlines Flagship Lounges, you can get away from the busy terminal and enjoy a little peace and quiet before or after your flight. And when you travel in our First Class cabin on an American Airlines International Flagship Service flight, it’s yours to enjoy with our compliments. We also invite our oneworld® Emerald and international customers to use the Flagship Lounges when traveling on eligible oneworld flights.

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