When you check in, one of three things may occur if you were unable to select an E- seat beforehand:

1. An E- seat will have opened up for some reason, and you will be put in it.
2. All of the E- seats are full, but an E+ seat is open, and you will be put in it, even if you do not pay for the buy-up-to-E+ offer (if you do pay, you will get to select which open E+ seat you get).
3. All of the seats are full (overbooked), and you will be on standby with the possibility of IDB.