The industry standard for citations between scholarly publications is CrossRef, which is the official DOI link registration agency for scholarly and professional publications. I don't know what the original document said, but if it was a scholarly publication, the citation should/could have been done by DOI. DOIs resolve to URLs, but publishers have a mandate to keep them up-to-date.

http://crossref.org http://en.wikipedia.org/wiki/Digital_object_identifier http://www.doi.org/

(I work for CrossRef)