The persons concerned shall keep the documents referred to in Article 14 for the purposes of control by the customs authorities, for the period laid down in the provisions in force and for at least three calendar years, irrespective of the medium used. That period shall run from the end of the year in which: ... (b) in the case of goods released for free circulation at a reduced or zero rate of import duty on account of their end-use, from the end of the year in which they cease to be subject to customs supervision ...
