Article 9 Montreal Convention
Article 9 of the Montreal Convention (Convention For the Unification of Certain Rules for International Carriage by Air) is titled Non-compliance with Documentary Requirements. It is under Chapter II (Documentation and Duties of the Parties Relating to the Carriage of Passengers, Baggage and Cargo).
Non-compliance with the provisions of Articles 4 to 8 shall not affect the existence or the validity of the contract of carriage, which shall, nonetheless, be subject to the rules of this Convention including those relating to limitation of liability.
See also: Article 8 Montreal Convention