I can't figure out where airlines get their mileage distances from. It can be important for programs that award EQP based on zones (eg. QF). On BA's LGW-KEF flight, the great circle calculator shows 1205 miles (which is QF zone 3) but it only credits as ~1180 miles (zone 2). They seem to be using LHR-KEF mileage in this case. Maybe AA still is using mileage from Kai-Tek?