The declaration was published as an addendum to that text. It says that as the Council was intended to be “pastoral”, it should not be understood to be infallibly defining any matter unless it openly says so (which it never did).
*“In view of the conciliar practice and the pastoral purpose of the present Council, this sacred Synod defines matters of faith or morals as binding on the Church only when the Synod itself openly declares so.” (Walter M. Abbott, SJ, The Documents of Vatican II, p. 98)
*
Paul VI again highlighted the non-infallible, non-definitive character of Vatican II in a general audience a year later.
“There are those who ask what authority, what theological qualification, the Council intended to give to its teachings, knowing that it avoided issuing solemn dogmatic definitions backed by the Church’s infallible teaching authority. The answer is known by those who remember the conciliar declaration of March 6, 1964, repeated on November 16, 1964.** In view of the pastoral nature of the Council, it avoided proclaiming in an extraordinary manner any dogmas carrying the mark of infallibility**.” (General Audience, December 1, 1966, published in the L’Osservatore Romano 1/21/1966)
That is plain: Vatican II “avoided issuing solemn dogmatic definitions backed by the Church’s infallible teaching authority”; it “avoided proclaiming in an extraordinary manner any dogmas carrying the mark of infallibility”. The documents were intended to be of the ordinary but not universal magisterium, called the merely “authentic magisterium” in the 1983 Code.
Paul VI confirmed again in 1975 that Vatican II was pastoral and not an infallible dogmatic council.
“Differing from other Councils, this one was not directly dogmatic,** but disciplinary and pastoral.” (General Audience, Au**gust 6, 1975)