With regard to products which had a type-certificate issued or validated by a Member State before 28 September 2003, the product in Principle is deemed to have a type-certificate issued in accordance with Commission Regulation (EC) No 1702/2003. In such cases where more than one TCDS for the same product existed within the Member States (e.g. TCDS of the State of Design and TCDS of another Member State having validated that TC), the Agency used the TCDS of the Member State of Design as basis for its TCDS in most cases. If the EASA-TCDS differs from one of the grandfathered TCDS, the owner is not required to modify the product retroactively, provided that the circumstances of Article 2a of Commission Regulation (EC) No 1702/2003 are fully met with. Any future Regulation on air operation may however require the installation of other or additional equipment.