CG aft of the CP, or the AC (aerodynamic centre), isn't a stability issue.
Longitudinal stability is determined by the static margin (cg to neutral point) and manoeuvre margin (cg to maneouvre point). Both of these are determined for the entire aircraft configuration i.e. "tail on".
Normally one talks of the CP or AC as "tail off".
The NP/MP are "always" aft of the AC, so the CG may be aft of the AC/CP and the aircraft remains stable.
25% MAC is a good approximation for the CP of the wing (that's why it came into use), and the fuselage tends to pull the wing-body CP/AC forwards. Yet many aircraft have an aft cg limit well past 25% MAC, with no stability issues, because the tail is doing what it's there for.