I', not sure. but in my mind, when I think of Aces, I think of Bob Gibson, Juan Marichal, Ferguson Jenkins, etc. An Ace to me, was the kind of pitcher who was going to win most of the time, and dominate most of the pitcher/hitter match-ups. An Ace was described as someone who could show you something special every time they took the mound, i.e. shutout, big strikeout total, no-hitter, etc.