Originally Posted by Nogbad

Why not just have the crediting FFP number on your BP to start with, and just use for A3*G for lounge access? Well, by having your A3*G number on your booking at check-in ensures you get all *G check-in/luggage perks. And with your A3 number on your BP when you access the lounge you meet even the strictest interpretation of the A3 T&C. Additionally, sometimes you get lounge invites at check-in or just invitations printed on your BP - it is then much quicker to enter the lounge, rather than having hand over your A3 card again, explain that Aegean is really a *A airline, show them it is listed on the wall, and wait for them to type it in and wait for computer say yes. Also, there are rumours that some airlines block seats next to *Gs. So I think it makes more sense to initially associate your BP with your A3*G number when booking and change the crediting later if needed for that flight.