curious about eligibility:
Traveling First Class onboard an international American or select oneworld alliance® carrier* anywhere in your outbound itinerary*Eligible oneworld alliance carriers include, British Airways, Cathay Pacific, Japan Airlines and Qantas. These carriers offer an international First Class service, which is defined as First Class service onboard a three-class (i.e. First, Business and Main Cabin) or four-class (i.e. First, Business, Premium Economy and Main Cabin) aircraft.

could this include tickets such as AONEX that have F flights later in the itinerary (outbound from US, but not same-day)? for example Day 1 DFW-JFK on AA in D, then 1 week later JFK-NRT on JL F. Could you use the Flagship checking in DFW?
probably not, but the wording is ambiguous