Originally Posted by findark

If the flight is J4, it generally means there are four seats available in Polaris after any oversales have been resolved by op-ups (maybe three sometimes, although that's rare). So the first four (or three) people on the list, from any cabin, will be cleared in order of the list.

Separately, op-ups may need to run to resolve the oversale, but that is shuffling assignments into inventory that is already blocked (i.e. not into J space). It's rare enough, especially with the multiple lower cabins, that I don't know how it will play out in practice here.