(4) If exceptionally, in the course of the frontier controls, the sequence of operations provided for in paragraph (1) of this Article is modified, the officers of the State of arrival may not proceed to detentions, arrests or seizures until the frontier controls of the State of departure are completed.In such a case, these officers shall escort the persons, vehicles, merchandise, animals or other goods, for which the frontier controls of the State of departure are not yet completed, to the officers of that State.If these latter then wish to proceed to detentions, arrests or seizures, they shall have priority.