Best janitor I've experienced would replace low rolls with new and then set the low roll on top of the dispenser. Of course, the dispenser was the correct shape to allow for that
Around here, public toilets have roll holders containing 2 rolls. 2nd is unreachable, but when the 1st is empty, it falls out and 2nd drops in its place. Janitors just fill the 2nd roll if missing.
I am hoping this is normal around the world and nobody throws away slightly used rolls.