It was not a case of United figuring out how good Nini is, it was a case of Nani figuring out how good is he, and figuring that talent alone is not everything and that working and training hard pays off.
I always believed in Nani but he was really poor before last year. Since his first game we know how talented he is, but he was very inconsistent.
In his 2nd he stalled and got played much less and in his 3rd season (09/10) he was playing so poor till the point that most of our fans wanted him out, he got injured and then in january 2010 he returned. Fergie played him against Wolves, he had a decent game and then played him against Hull and once against impressed and gained himself a start against City, which once again he impressed and then the game against Arsenal came and that moment Nani defined himself.
Fergie always knew how talented Nani is, but it was Nani to blame for not playing good. Nani said that with all the talks of him leaving the club in January he thought he must improve, he said that he was very disappointed for not being good enough. Fergie had a word with him and told him that he still trusts and believes in him, and since then Nani started training more. working harder and playing better, he even started to track back.
Nani changed so much in 2010.