you always have to change before you purchase a ticket to see whether that booking class is eligible for mileage accrual. under every FFP, whether it's oneworld or star or skyteam or any other airline, there's always fineprint at the bottom saying mileage accrual only on eligible booking classes. most airline websites have a chart telling you which booking classes for which of its airline partners are eligible for mileage accrual. you should check them out first...