A year ago, I wanted to do a short film adaptation of an argentine short story (published in 56.) I contacted the agents managing the literature of the author in spain(The author passed away in 84.) They briefly told me that the audio visual rights were not available at that moment. What do I need to do to legally make this short film? Anything I can ask for or offer to give the agency back? Anyone know when such a story would become public domain? I have my script adaptation to at least come at them with some work prepared this time.