It is the airplane's aerodynamic center that matters.
The 25% of MAC applies to the wing, only. If you include al the other elements (fuselage, nacelles...) then it is somewhere else. Then you have to put the CG ahead of it.
Normally, airplanes would be unstable if they had no tailplane (AC ahead of CG), but the great effect of the tailplane (also called stabilizer) makes the airplane estable, as a whole. Otherwise the airplane would be inefficient (large negative lift at the tailplane).
I think that in the case of the 320 all these things about stabiilty are complicated if we consider normal law because we cannot even talk about stick free or stick fixed... but I have the idea that 320s are less stable than similar conventional flight control airplanes, which makes them more fuel efficient. Normal control law augments their stability by means of the computers.