As for me, I talk about plat as that is the only status I have monitored. I think there will be different answers depending on who you are asking. I am sure we can find silvers or even statusless that can attest to seat block working.

IME from the past, lower tier members, especially juniors, are sometimes blocked from choosing any seat. Yes, seat selection is free of charge when OLCI opens, but all seats except the one AY assigned them are marked as taken.