Lots of seats are blocked once OLCI opens. Being 7th person checked in does not mean that seat block will remain as more people check in. having status gives a good chance of the block remaining.

What I do not know is what the algorthim is that frees seats up. Does two golds on separate bookings in A and C mean that B is less likely to be freed up that C would if A and B was a couple, both Gold travelling together on one PNR. Does 2 silvers trump 1 gold etc etc....

Watch the seat blocks change on a few flights, especially in the last two hours before check in closes. It is very very dynamic.

At any one time only a small number of seats are shown as available at any one time, so people without status have very little choice when they check in, while status customers have more choice to pick seats before check in opens.