I get that, but the system is a joke. The final whistle is either the final whistle or it isn't.
Incidentally I remember a CL game where we "won" a last second penalty but it wasn't given because the ref blew for full time. Ref said afterwards he would have given it "but there was no time", but It was determined afterwards by those who know the rules better than I do that because the penalty incident occurred before the whistle had blown, it should have been given. If I'm not mistaken that would have given us a draw which would have been enough to progress. Can't remember the exact match or circumstances though.