Sorry Tony, but no matter how you format the same date in different cells, when you compare these cells with a formula will say they are equal, except the case when one of the cells is formatted as text...
if this is the case here, the problem can be solved converting text in date, with : =DATE(RIGHT(L16;4);MID(L16;4;2); LEFT(L16;2)), where L16 is the cell containing date formatted as text; only now you can correctly compare dates ...