I just googled it, and 1976 seems to be the common release date, but without any references. On this page[1], it says that BSD (1977) had ex, and 2BSD includes vi, so that would make the first public release 1978.

Considering the age of Unix, calling vi new in 1984 would still make little sense, but maybe the book mentioned was actually written long before that date.

[1]: http://oreilly.com/catalog/opensources/book/kirkmck.html