We booked a cheap premium economy seat (with a lap infant) from ORD to MAD. I am not an Iberia plus member (I'm crediting the flights to AA due to the superior EQDs/EQMs you can receive for non AA metal partner flights). Generally, do you need to be an iberia plus member and have that number attached to the reservation to get the cash upgrade offers? Should I wait until check in? I see 5 seats available in biz according to expert flyer. If I do need to be an iberia plus member, should i sign up and then can change the FF# attached to the flight at a later date or at airport check in?