Art. 93 CISG
(1) If a Contracting State has two or more territorial units in which, according to its constitution, different systems of law are applicable in relation to the matters dealt with in this Convention, it may, at the time of signature, ratification, acceptance, approval or accession, declare that this Convention is to extend to all its territorial units or only to one or more of them, and may amend its declaration by submitting another declaration at any time.
(2) These declarations are to be notified to the depositary and are to state expressly the territorial units to which the Convention extends.
(3) If, by virtue of a declaration under this article, this Convention extends to one or more but not all of the territorial units of a Contracting State, and if the place of business of a party is located in that State, this place of business, for the purposes of this Convention, is considered not to be in a Contracting State, unless it is in a territorial unit to which the Convention extends.
(4) If a Contracting State makes no declaration under paragraph (1) of this article, the Convention is to extend to all territorial units of that State.
Overview of case law on Art. 93 CISG: UNCITRAL Digest
The UNCITRAL Digest on the CISG can be used as a starting point to discover the relevant case law on this article.