Yes, there is a difference between BAEC members getting free seats - which they see during the booking process so long as they are logged in - to other oneworld members. Because AS members won't be logging into BAEC beforehand, you need to have the reservation fully in place and then go in for the free seats. When you initially book, you may well add your AS card number, but you are still in the outer world where seats are chargeable. so you must ignore those screens. Once you are booked, your status is then confirmed and with it seating rights.