It was not until late in the summer of 2012 that Jacob deGrom made what baseball development professionals consider one of a prospect’s most significant leaps, the move from Class A to Class A Advanced. The last of a sizeable group of future Mets to reach that level, deGrom was a ninth-round pick with an improving fastball and a telltale scar on his right elbow, resting perpetually near the fringes of prospect radar screens.