In Conte de fées (Passé Composé vs Imparfait) we're given the clue so his daughter had to take care of the garden and the animals. with 'devait' given as the correct answer and not 'a dû'. Why is that the case, when in this class it seems to be the opposite way around? It follows the context of her father rarely leaving his bed, and is followed by describing something she would also do once a month. So it seems unlikely to fit the 'we don't know if she fulfilled that obligation' case for using devait.