Booking and confirmation
Applying does not guarantee a seat. Your seat is confirmed when ExCo successfully receives the first payment required for your edition. The confirmation email records the booking but is not an extra condition.
Your confirmed seat and the edition's status are different. An available edition is open for booking but is not yet guaranteed to run. A confirmed edition is guaranteed to run.
Seat availability is separate again. If an edition reaches its maximum spots, it moves to On Request and you may join the waitlist for free. An unavailable edition is cancelled or finished and cannot be booked.