4O the sword and Stun Up (NieR: Automata)

Who can knows, how it works stat Stun Up on the sword 4O or whatever. Not that I doubted that the stun proc from attacks, but starting over 9S had doubts. Dropped the chip on stun and I thought, maybe this stat on the sword adds the effect to the chip? Using hacks? How to check this or is it definitely wrong?