Good question Ann. I have always wondered the same. For LatAm Spanish, it feels like another nuance that could go either way depending on context or emphasis. Just my 2 cents without knowing the definitive answer. 

I've come to the conclusion that without more specific hints, such as which region or the distance in time, it is just not possible to answer these questions correctly. You have to either ignore the grade or memorize the question and answer.

I've come to the conclusion that without more specific hints, such as which region or the distance in time, it is just not possible to answer these questions correctly. You have to either ignore the grade or memorize the question and answer.