Too old to be a ‘foundling’? – International standards and comparative analysis – B. Legislation and Legal Precedents of State Parties as Supplementary Means of Interpretation The ILC’s Draft Conclusions on Subsequent Agreements and Subsequent Practice in Relation to the Interpretation of Treaties of 2018 (‘2018 ILC Draft Conclusions on Subsequent Practice’ or ‘Draft Conclusions’),32 Conclusion 5(1) clarifies what constitutes ‘subsequent practice’ both under Article 31 (3) (b), and also as ‘supplementary means of interpretation’ under Article 32 of the VCLT: Subsequent practice under Articles 31 and 32 may consist of any conduct of a party in the application of a treaty,33 whether in the exercise of its executive, legislative, judicial or other functions (emphasis added).34 It is thus clear that domestic legislation as well as administrative and judicial precedents in the implementation of a treaty may constitute ‘subsequent practice’ both under Article 31(3)(b) and Article 32. However, establishing that subsequent practice shows ‘agreement of the parties’ under Article 31(3)(b) of VCLT is more challenging. The Draft Conclusion 10(1) notes that an ‘agreement’ under Article 31(3)(b) requires ‘a common understanding regarding the interpretation of a treaty which the parties are aware of and accept’. Nevertheless, as paragraph 9 of the Commentary to the Draft Conclusion 2(4) states, subsequent practice in the application of the treaty, which does not meet the high standard of Article 31(3) (b), but establishes the agreement of only one or more parties, may be used as a ‘supplementary means of interpretation’ under Article 32 of the VCLT35 which may, according to Draft Conclusion 7(2), ‘contribute to the clarification of the meaning of a treaty’.36 The review of foundling provisions around the world, as well as judicial decisions in some states, in this article will thus be utilised to identify subsequent practice either under Article 31 or 32 of VCLT. C. Relevance of Practice of Non-State Parties - Nationality Granted to Foundlings as Customary International Law It should first be noted that, as summarised in Table 1, among the 142 states that have domestic foundling provisions as of February 2026, 77 states, or approximately 54%, are not, in fact, state parties to the 1961 Convention. In addition to the laws and practice of state parties to the 1961 Convention, this article refers to nationality laws and legal precedents in several non-state parties to the 1961 Convention, such as Japan,37 France and the USA. This is because the article asserts that Article 2 of the 1961 Convention codifies a customary law norm granting nationality to foundlings that had already existed at the time the Convention was drafted.38 32 ILC, ‘Draft Conclusions on Subsequent Agreements and Subsequent Practice in Relation to the Interpretation of Treaties with Commentaries’ in Report of the International Law Commission, A/73/10 (70th session, 2018) <https://legal.un.org/ilc/texts/1_11.shtml>. 33 It is noted that the ILC Commentary on the Draft Conclusion 4 at paragraph 18 states ‘the enactment of domestic legislation (... ) for the purpose of implementing a treaty’ constitutes ‘subsequent practice’, thus it is arguable that nationality law provisions that had already existed before a particular country’s accession to the 1961 Convention might not count as ‘subsequent practice’. Nevertheless, it is recalled here that Article 2 of the 1961 Convention (foundling provision) is a codification of a principle already common in nationality laws around the world at the time of drafting. It is thus reasonable to refer to nationality laws adopted before the countries’ accession to the 1961 Convention as ‘subsequent practice’. 34 See also for example Irina Buga, ‘The meaning of “practice”, in Modification of treaties by subsequent practice (OUP 2018) 25. 35 See also Goodwin-Gill, ‘The Search’ (n 16) 210, and Dunlop, ‘Applying the Rule of Treaty Interpretation’ (n 16) 57 among others. 36 Goodwin- Gill promotes a third way of charactering the interpretative value of domestic judicial decisions, i.e. as ‘subsidiary means for the determination of rules of law’. under Article 38(1)(d) of the ICJ Statute. Goodwin- Gill, ‘The Office of the United Nations High Commissioner for Refugees and the Sources of International Refugee Law’ (‘Sources’) 69 International and Comparative Law Quarterly 1(2020) 31. 37 Japanese courts have issued several judgments and rulings that are considered exemplary at the global level, as referred to in sec 3 and 4 below. See Shoichi Kidana, Chikujo kokusekiho – Kadai no kaimei to jobun no kaisetsu [Nationality Act on an Article-by-Article Basis – Clarification of Issues and Commentaries on the Articles] (Nihon kajo shuppan 2021) 319-329. See also Yasuhiro Okuda, Kazoku to kokuseki [Family and Nationality] (Akashi Shoten 2017); Ayane Odagawa and Sosuke Seki eds., Typology of Stateless Persons in Japan (UNHCR Japan 2017) <https://www.refworld.org/reference/countryrep/unhcr/2017/en/121868>. 38 This was also already asserted (‘arguably’) by Laura van Waas, Nationality Matters (Intersentia 2008) 70-71 and 90. European University Institute 12