Our rule of thumb is when in doubt, throw it out, however living here I have caught a bit of the paranoid bug about dates - can't explain why the natives have it but I know for me since I am not quite sure how they determine what (even though logically it will be along the same lines of back home), I just think it's better to err on the side of caution. Like the way things are done here still has this impenetrable mystery to it - totally irrational way to think, I know.