Until the dates of the upgrading of the NCTS referred to in the Annex to Implementing Decision 2014/255/EU, where the paper-based Union transit procedure for goods carried by air or sea is used in accordance with Article 24(1) of this Regulation, the proof of the customs status of Union goods shall be provided by entering the letter ‘C’ (equivalent to ‘T2L’) alongside the relevant items on the manifest.