Rotation is a control, not an arrangement
In any store holding dated consumables, the physical position of stock carries information. Front means use first. Behind means later. That is the entire mechanism, and it works because everybody who touches the shelf understands it. A person who does not know the convention, who tidies a shelf so it looks neat, has just reversed the order without leaving any trace of having done so.
That is why the rule has to be absolute rather than a matter of judgement. It is easy to state, easy to induct and easy to check. It also removes any ambiguity about responsibility: if stock has been rotated incorrectly, it was not the cleaning contractor, because the scope says clearly that cleaning does not touch stock at all. It also spares staff from wondering whether an unexpected arrangement was theirs or somebody else's.
