How the rounds work

Allocation runs in rounds. In each round, seats are offered against the current lists; people accept, decline or upgrade; seats freed by those decisions are re-offered in the next round. This is why a seat that was out of reach in round one can become reachable in round three, and why leaving the process early is expensive.

The mechanics of accepting differ by system, but the shape is consistent: you generally either freeze a seat, meaning you keep it and stop, or float, meaning you keep it while remaining in the running for something higher on your list. Understanding which one you are choosing, before the deadline rather than during it, is most of the skill.