The International Law Commission (ILC) of the United Nations is a subsidiary organ of the General Assembly (GA), and has the task of codification and progressive development of international law. In its recent Annual Report to the GA (Supplement No. 10, UN Doc.   A/69/10), the ILC included, inter alia, the text of draft conclusions 6-10, and the related commentaries, on the topic of 'subsequent agreements and subsequent practice in relation to the interpretation of treaties'.

In its Commentary, the Commission endorsed the interpretation given by Professor Skordas to Art. 5 of the 1951 Refugee Convention (A. Zimmermann ed., The 1951 Convention relating to the Status of Refugees and its 1967 Protocol: A Commentary, OUP 2011, p. 682, para. 30).  According to this interpretation, the complementary protection of persons in refugee-like situations is not practice ‘in application’ of the Convention. By adopting this perspective, the ILC was able to distinguish ‘subsequent practice’ in the meaning of Art. 31(3) Vienna Convention on the Law of Treaties, from other conduct or developments in the wider context of a treaty under interpretation (ILC Annual Report, p. 173, paras. 9-10).

You can find the ILC Report in: http://www.un.org/law/ilc/