http://www.oxforddictionaries.com/definition/english/correspondence exemplifies only the singular noun and http://www.grammarphobia.com/blog/2008/10/correspondence-course.html claims:
“Correspondence” is a singular noun for the letters and emails and so on that are exchanged by parties who communicate with one another. In ordinary English, it’s not used in the plural (“correspondences”). But “correspondents,” meaning people who correspond, is plural.
Does this contradict https://www.google.com/search?q=%22correspondences+via+email%22&btnG=Chercher+des+livres&tbm=bks&tbo=1&hl=fr&gws_rd=ssl#hl=fr&q=%22email+correspondences%22&tbm=bks, which yields >10 pages for "email correspondences"?
What's this phenomenon called? Are there any other nouns with it?