What i did :
Ability set as passive that apply a status effect 'A'.
The stat effect 'A' use a Game Event on Turn Start.
The Game Event should add 1 stack of status effect 'B' & 'C' on the user for each enemies in battle :
Store Combatant Count > Game Variable Fork > Change Status Effect > Debug
Everything seems to work the way i want except the Change Status Effect node who is used as many times as needed to cap the Max Stack Count of 'B' & 'C'.
i.e. : if 'B' has a max stack count of 42, i then have 43 Debug printed.
Side question : is there a Sub Type category for Status Effect like there is for Combatant ?