So, Duo seems to accept two different English translations here for "Eu não vi";
1.) "I have not seen..." 2.) "I did not see..."
In English, there is a subtle difference in the meanings: the first ("I have not seen...") implies that I last saw my father one year ago and have yet to see him since; the second ("I did not see...") implies that in the past there was a full year in which I did not see my father, but since then, things have changed (e.g., "I did not see my father for a year, but we have since rekindled our relationship.", or "I did not see my father for a year, and then he passed away.")
Does "Eu não vi..." actually cover both of these cases, or only one?
In English we can say something like, "I haven't seen my dad for a year, but now he's here visiting me." My Portuguese friend gave me that context for when you could have the "haven't seen" translation for this sentence. So, to the Portuguese mind the time period has ended (dad's here now), but the English sense of present perfect is a bit more flexible.