Excerpt from John O. Honnold, Uniform Law for International Sales under the 1980 United Nations Convention, 3rd ed. (1999), page 540. Reproduced with permission of the publisher, Kluwer Law International, The Hague.
The Convention does not have retroactive effect. Under Article 100(1) the rules on formation of the contract (Parts I and II of the Convention) are applicable only when "the proposal for concluding the contract" is made on or after the Convention enters into force for the relevant Contracting State or States. Under Article 100(2) the rules governing the rights and obligations under contracts (Parts I and III of the Convention) are applicable "only to contracts concluded after the date when the Convention enters into force" for the relevant Contracting State or States.
Paragraphs (1) and (2) both refer to entry into force "in respect of the Contracting States referred to in subparagraph (1)(a) or the Contracting State referred to in subparagraph (1)(b) of article 1." The effect of this dense language can be understood with the help of an example suggested by the helpful discussion by Evans in B-B Commentary 673–674.
Example 100A. The Convention entered into force for State A on March 1, 1990 and for State B on May 1, 1990. (These dates reflect the twelve-month period following the deposit of the instrument of adoption specified in Article 99). On April 20 Seller in State A by telex made a "proposal" (which for the present we shall assume was an "offer") for a sales contract to Buyer in State B. On May 10 Buyer by telex transmitted an "acceptance" to Seller. Does the Convention (Parts I and II) govern the question whether these communications concluded a contract?
The problem is complex since Article 100(1) provides that applicability may be derived from either (A) Article 1(1)(a) ("Sub(1)(a)" or (B) Article 1(1)(b) ("Sub(1)(b)").
(A) Can applicability of the Convention be based on Sub(1)(a)? The answer is No since the Convention had not entered into force "in respect of the Contracting States referred to" in Sub(1)(a). Sub(1)(a) makes the Convention applicable only when the States of both parties "are Contracting States"; at the time of the offer the Convention was effective only in State A.
(B) However, the Formation rules of the Convention may yet apply if the Convention was in force on April 20 (the date of the offer) "in the Contracting State referred to" in Sub(1)(b)—i.e., the Contracting State designated by "the rules of private international law". If these rules designate State B the answer is still No, since the Convention became effective in State B only on May 1; if the rules designate State A (effective date March 1) the Convention applies.
Paragraph (2) of Article 100 on the effective date for obligations under the contract (Part III of the Convention) uses the same approach as paragraph (1) on formation; the above illustrations based on paragraph (1) apply to paragraph (2), mutatis mutatandis. [page 540]
FOOTNOTES: Chapter on Final Provisions
18. If the States in question had made a declaration under Article 95 excluding Sub(1)(b) the answer could end here.
19. In Example 100A the communications were transmitted by telex. If the communications (e.g.) went by post and were subject to delay it may be necessary to refer to Article 15(1) (an offer "becomes effective when it reaches the offeree") and Article 18(2) (an acceptance becomes effective when it "reaches the offeror". Although these rules may lead to the conclusion that the Convention does not apply it seems necessary to use the Convention’s own rules to apply its rules on applicability.