In my experience it is a forever changing process. It used to be the case seatmaps opened up at a certain point pre flight so that you could choose where you sat. Last time we had no choice in the matter and were flubgraded T-24 and without the ability to move around or back to where we had come from. The seat map just wasn't there. Nor could check in move us around/back to regular Club. Only on board was it apparent Flub was half full with regular Club about the same. Definitely seemed to be status driven and something nobody other than the flight management gods had any control over.