55Moreover, it should also be borne in mind that, according to that same line of case-law, whilst the principle of legal certainty precludes a regulation from being applied retroactively, namely to a situation which arose prior to the entry into force of that regulation, 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. However, if the new law is thus valid only for the future, it also applies, save for derogation, to the future effects of situations which came about during the period of validity of the old law (see, inter alia, judgment of 3 September 2015 in A2A, C‑89/14, EU:C:2015:537, paragraph 37 and the case-law cited).
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