I can't remember if 3U does it, but I know for normal 2U subjects they can look at your extension results to split people who tie (it says this some where on the board of studies website).
Cause usually a lot of people who get state have the same marks as each other (like more than 20 but less than 50) so they look at the corresponding 2-unit or 4-unit marks and decide which get state ranks for overall performance and which don't.