In certain cases, A0 does not mean there are no first class seats available, just that the airline is not willing, at that time, to let them go to those flying on A class. When you have top status the agent taking your call can, if you are persuasive enough, and the agent is nice enough, and the stars are correctly aligned, talk to yield management and plead your case; if successful YM will release one seat (A0 becomes A1) and that seat is assigned to you. Without status this already hard feat becomes mission impossible.