I think you have to do two qualifying vaults, each different. Alicia Sacramone was the only one before who did the 2 vaults from the US before. At worlds, Kayla Williams was the only one from the US to do two. Since the AA only requires one vault, a lot of gymnast only train and compete one vault, not two. To qualify for Vault, they average the two vaults, so although someone was higher scored that Kayla Williams on vault, they only competed one vault so she was the highest scoring with two vaults. It seems a lot of vaulters specialize in vault and floor. Not many seem to do AA.