In that context, Article 236 of the Customs Code cannot be interpreted as prohibiting the Commission from directing that a ruling be made on the applications for repayment of those anti-dumping duties following a procedure with the specific aim of allowing it to calculate such a difference.

In view of those grounds, it must be held that, in order to comply with the obligation to implement the judgment of 4 February 2016, C & J Clark International and Puma ( C‑659/13 and C‑34/14 , EU:C:2016:74 ), the Commission was entitled to take the view that the onus was on it to carry out an assessment of the claims submitted by the exporting producers concerned with a view to determining whether the anti-dumping duties that applied to them under the definitive regulation and the prolonging regulation should have been set at rates below those laid down by those two regulations.

However, the exact scope of a declaration of invalidity by the Court in a judgment and, consequently, of the obligations that flow from it must be determined in each specific case by taking into account not only the operative part of that judgment, but also the grounds that constitute its essential basis (see, to that effect, judgment of 28 January 2016, CM Eurologistik and GLS, C‑283/14 and C‑284/14 , EU:C:2016:57 , paragraph 49 and the case-law cited).

Indeed, it is settled case-law that, when the Court declares that a regulation imposing anti-dumping duties, such as the definitive regulation or the prolonging regulation, is invalid, such duties are to be considered as never having been lawfully owed within the meaning of Article 236 of the Customs Code and, in principle, are required to be repaid by the national customs authorities under the conditions set out to that effect (see, to that effect, judgments of 27 September 2007, Ikea Wholesale, C‑351/04 , EU:C:2007:547 , paragraphs 66 to 69 , and of 18 January 2017, Wortmann, C‑365/15 , EU:C:2017:19 , paragraph 34 ).

In that regard, first, in respect of the possibility of resuming the proceeding at the origin of the definitive regulation and the prolonging regulation with the aim of re-imposing the anti-dumping duties imposed by those regulations during their initial application period, it must be held that where a judgment of the Court annuls a regulation imposing anti-dumping duties or declares such a regulation to be invalid, the institution called upon to take such measures for the purpose of implementing that judgment does have the option of resuming the proceeding at the origin of that regulation, even if that option is not expressly set out in the applicable legislation (see, to that effect, judgment of 28 January 2016, CM Eurologistik and GLS, C‑283/14 and C‑284/14, EU:C:2016:57, paragraphs 51 and 52). In addition, it follows from settled case-law that, except where the irregularity found has vitiated the entire proceeding with illegality, the institution concerned has the option, in order to adopt an act intended to replace the act that has been annulled or declared invalid, to resume that proceeding only at the stage when the irregularity was committed (judgment of 28 January 2016, CM Eurologistik and GLS, C‑283/14 and C‑284/14, EU:C:2016:57, paragraph 51).

Second, as regards the question of whether such a resumption of the proceeding is authorised in a case in which the anti-dumping rights at issue have expired, in view of the rules that apply in respect of non-retroactivity, it follows from the case-law of the Court that, when an institution of the European Union chooses to use its option to resume the proceeding referred to in paragraphs 73 and 74 of this judgment, it must, in accordance with the principles governing the temporal application of the law, comply with the substantive rules in force at the time of the facts referred to in the regulation that was annulled or declared invalid (see, to that effect, judgment of 14 June 2016, Commission v McBride and Others, C‑361/14 P, EU:C:2016:434, paragraph 40).

Thus, in accordance with Article 10(1) of Regulation No 384/96, the resumption of the proceeding effected in the present case by the regulation at issue cannot result in the reimposition by the regulation adopted at the end of that proceeding, as a replacement for the definitive regulation and the prolonging regulation, of the anti-dumping duties that would be applied to goods released for free circulation prior to the date on which those regulations entered into force. However, the wording of Article 10(1) of Regulation No 384/96 does not preclude such a resumption of the proceeding in a case in which the anti-dumping duties concerned have expired since that date, provided that such duties are re-imposed during their initial application period, and therefore, in the present case, with regard to goods put into free circulation after the entry into force of the definitive regulation and the prolonging regulation.

Finally, with regard to the rule set out in Article 221(3) of the Customs Code, it must be noted that its effect is indeed not only to prevent the amount of duty from being communicated to the debtor after the expiry of the three-year period from the date on which its customs debt arose, but also to time-bar the customs debt itself upon the expiry of that time limit (see, to that effect, judgment of 23 February 2006, Molenbergnatie, C‑201/04, EU:C:2006:136, paragraphs 39 and 41).

However, as the Court has already held, that rule applies, according to the wording of Article 221(3) of the Customs Code, only to the communication of the amount of duty to the debtor, and its implementation, in that respect, is a matter for the national customs authorities alone, who are competent to make such a communication (see, to that effect, judgment of 13 March 2003, Netherlands v Commission, C‑156/00, EU:C:2003:149, paragraphs 63 and 64).

(see paras 73, 74, 76-78, 80, 81)