Treaty law is a high specialized field of study. Technically, “the law of treaties” refers to how treaties are created, whereas “treaty law” focuses on the subject of these treaties.

Some people however, have the mistaken impression that treaties are like chain letters, that one country receives a document to sign after another one, and that everyone is referring to what has already been done elsewhere! In actual international legal theory and practice, an instrument is first drafted and adopted. If there is a signature event, it is possible that several States will sign the actual text or an instrument of approval (which has the same legal effect) on the same day, or within a short time.

Note: the definition of “chain letter” is:

Every treaty contains a clause indicating when it enters into force, and after how many signatures. The key idea is that a single text is approved by one State after after another, with the result that a State can approve a treaty that was signed by other States 50 years before. A treaty enters into force under international when it entered into force for the States that have approved it.

A good example is the treaty that established the University for Peace which is now headquartered in Costa Rica:

STATUS AS AT : 08-11-2013 07:51:55 EDT
6 . International Agreement for the Establishment of the University for Peace
New York, 5 December 1980
Entry into force
7 April 1981, in accordance with article 7.
Registration :
7 April 1981, No. 19735
Status :
Parties : 40
Text :
United Nations,  Treaty Series vol. 1223, p. 87; and C.N.1127.2001.TREATIES-3 of 1 November 20011.
Note :
The Agreement was adopted by resolution 35/552 of the General Assembly of the United Nations dated 5 December 1980. It was open for definitive signature by all States at the United Nations Headquarters in New York from 5 December 1980 to 31 December 1981.
Participant Signature Accession(a), Succession(d), Definitive signature(s)
Argentina 29 Dec 1997 a
Bangladesh  8 Apr 1981 s
Bosnia and Herzegovina 3   1 Sep 1993 d
Cambodia 10 Apr 1981 s
Cameroon 16 Aug 1982 a
Chile  2 Mar 1981 s
Colombia 18 Mar 1981 s
Costa Rica  5 Dec 1980 s
Cuba  9 Aug 1985 a
Cyprus 15 Mar 1983 a
Dominican Republic 21 Nov 1983 a
Ecuador 18 Mar 1981 s
El Salvador  7 Apr 1981 s
Guatemala 14 Sep 1981 s
Guyana  9 Aug 2001 a
Honduras 10 Apr 1981 s
India  3 Dec 1981 s
Italy 27 Nov 1981 s
Liberia 16 Sep 2005 a
Mexico 15 May 1981 s
Monaco  9 May 2011 a
Montenegro 4  23 Oct 2006 d
Nicaragua  3 Apr 1981 s
Pakistan 30 Mar 1981 s
Panama 20 Mar 1981 s
Peru  9 Apr 1981 s
Philippines 20 Mar 1984 a
Republic of Korea 11 Jun 2010 a
Russian Federation 23 Dec 1987 a
Senegal  1 Apr 1981 s
Serbia 12 Mar 2001 d
Slovenia  6 Jul 1992 d
Spain 21 Apr 1981 s
Sri Lanka 10 Aug 1981 s
St. Lucia  2 Sep 1986 a
Suriname  3 Jun 1981 s
Togo  3 Jun 1981 s
Turkey 27 Nov 1995 a
Uruguay 19 Nov 1985 a
Venezuela (Bolivarian Republic of)  5 Dec 1980 s

It can be seen that the document in question was approved by a cluster of States in 1981 and that it entered into force in April 1981 because Article 7 required the approval of 10 States:

“The present Agreement shall enter into force on the date on which it shall have been signed or acceded to by ten States from more than one continent. For States signing or acceding after the entry into force, the Agreement shall enter into force upon the date of signature or accession.”

Obviously, this is not a “chain letter” with rather a well established practice by which a standardized agreement is circulated and approved either by signing of the actual text or by deposition of an instrument of approval.

In the case of EUCLID, the initial agreement (49006) entered into force upon second signature which is actually the standard and default practice, and acquired multilateral treaty status upon third signature. The updated agreement (49007) specified:

“This multilateral and open memorandum renews and updates the previous agreement already approved by 8 Participating Parties and it shall enter into force on the date of signature by two Parties.”