The Commission shall be empowered to adopt delegated acts, in accordance with Article 284, in order to determine:
(a)
the cases, referred to in Article 28(2), where a favourable decision addressed to several persons may be revoked also in respect of persons other than the person who fails to fulfil an obligation imposed under that decision;
(b)
the exceptional cases, in which the customs authorities may defer the date on which revocation or amendment takes effect in accordance with the second subparagraph of Article 28(4).