66It therefore follows from the wording of the first subparagraph of Article 2(5) of the basic regulation that the records kept by the party under investigation are the prime source of information in order to establish the costs of production of the product concerned and that the use of the data included in those records constitutes the rule and the adaptation or replacement of that data on another reasonable basis is the exception. Since a derogation from or exception to a general rule must be interpreted narrowly, it must be considered that the exception arising from Article 2(5) of the basic regulation must be interpreted narrowly (see, to that effect, judgment of 15 September 2016, PT Musim Mas v Council, T‑80/14, not published, EU:T:2016:504, paragraphs 68, 69 and 83).