There is no definition of the borders of Morocco within the text of the EU-Morocco Association Agreement of 1996, which entered into force on 1 March 2000.
In practice, for the purposes of application of the tariff preference provisions of the Agreement, the European Commission provides each member state with details of the relevant issuing offices in Morocco which are approved to authenticate tariff preference documents. If in doubt HM Revenue and Customs would refer any queries to the European Commission.