I would go with "below" for "al calce" and "participating parties" for "los que en ella intervinieron" for an idiomatic English rendering.

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Note added at 29 mins (2010-02-11 20:34:32 GMT)
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The agreement, after being approved by an extraordinary meeting of NTT DOCOMO's board of directors, was signed by the participating parties.

http://www.mwjournal.com/article.asp?HH_ID=AR_5745

The nature of collaborative arrangements with these organizations varies, and includes the following main types:

Formal arrangements, signed by the participating parties, according to which the collaborating organization either ...

http://www.ilaqh.qut.edu.au/Misc/Collaboration.htm

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Note added at 30 mins (2010-02-11 20:35:51 GMT)
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If the petitioner has entered into a postadoption contact agreement with the birth parent as set forth in Section 8616.5, the agreement, signed by the participating parties, shall be attached to and filed with the petition for adoption.

http://www.megalaw.com/ca/cacodelink.php?codelink=http://www...

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Note added at 32 mins (2010-02-11 20:37:11 GMT)
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For "al calce," see:

cal·ce

4. Central America, Mexico. foot, bottom (of a document)

http://education.yahoo.com/reference/dict_en_es/spanish/calc...