94It must also be borne in mind that, while the principle of legal certainty precludes rules from being applied retroactively, that is to say, to a situation which existed before those rules entered into force, and irrespective of whether such application might produce favourable or unfavourable effects for the person concerned, the same principle requires that any factual situation should normally, in the absence of any express contrary provision, be examined in the light of the legal rules existing at the time when the situation obtained, the new rules thus being valid only for the future and also applying, save for derogation, to the future effects of situations which came about during the period of validity of the old law (see, to that effect, judgments of 3 September 2015, A2A, C‑89/14, EU:C:2015:537, paragraph 37, and of 26 May 2016, Județul Neamț and Județul Bacău, C‑260/14 and C‑261/14, EU:C:2016:360, paragraph 55).
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