It only works on low firmwares from memory, later on Nintendo made it so it could still download updates from Nintendo zone spots (and normal wireless if you have a valid connection set on sysNAND, or an empty spot and a valid connection on emuNAND) and will prompt you to update and allow you to update even with parental controls set. This could be wrong, feel free to correct me, but I'm certain that after a certain firmware having parental controls is not sufficient on its own to prevent updating.