December is not over yet, so 'movies I've seen in December' is correct. ** Movies I've seen in December so far include 'Silent Wedding', 'Rosso como il cielo' and 'The girl with the Dragon Tattoo'. :)) (so far = from the beginning of December to now, Dec. 11th. : from the past to the present) ** However, when January 1st. comes around you can say 'Movies I saw in December were A B C and D ' because December will be finished. (finished past)