Many confused claims are made regarding the Second Vatican Council that must be put straight. The first of these is that the Council was not “ecumenical” but “pastoral.” The distinction here is meaningless because the two terms are orthogonal: ecumenicity denotes scope, pastorality aim. There is no contradiction in a Council being both pastoral and ecumenical and Vatican II was, arguably, both.
The second is that the Council taught nothing new. This is, as far as it goes, true. It never once explicitly invoked its apostolic authority in order to command the assent of the faithful to adhere to a newly-proclaimed doctrine. But more is often read into this claim than is justified: that the Council taught nothing new doesn’t mean it didn’t teach at all, which leads us to our third claim.
The third is that, since the charism of infallibility was never exercised, the Council is in no way binding on the faithful. This is, again, untrue, for two reasons: first, because infallibility determines the degree of certitude of the assent which must be given to a set of teachings, not whether or not such assent be given at all; and second, because the Council did, in fact, relate infallible teachings, though the infallibility of those teachings inheres due to Magisterial exercises that predate Vatican II. There is often a regrettable stink about postconciliar discourse of “if it ain’t infallible, I don’t hafta believe it” — call it the “spirit of Vatican I.”
So I reject, on the one hand, the claim that the Council was not ecumenical (it was, because its scope was universal); I accept the claim that it taught nothing new; yet I reject the claim that the Council’s teachings are fallible in toto by virtue of that fact.
The apparent contradiction between these positions resolves when you understand that the Council was primarily concerned with tactics, not strategy — not with teaching but with adapting the immemorial customs and traditions of the Church to the demands of modernity. In this sense, it certainly was “pastoral.” Hence,
In calling this vast assembly of bishops, the latest and humble successor to the Prince of the Apostles who is addressing you intended to assert once again the Magisterium (teaching authority), which is unfailing and perdures until the end of time, in order that this Magisterium, taking into account the errors, the requirements, and the opportunities of our time, might be presented in exceptional form to all men throughout the world. 
In other words, the Council is Magisterial, but its Magisteriality is being invoked primarily to re-express (and, in that sense, reform) teachings from of old in a way that is intelligible to modern man.
This blog thus takes for granted:
- That the Council was a legitimate ecumenical Council of the Roman Catholic Church;
- That the Council was largely concerned with prudential, not doctrinal, matters, and in this respect is non-Magisterial;
- That the Council is doctrinally infallible to the extent it expresses previously infallibly defined teachings; but that
- The re-expressions themselves are prudential adaptations.
A logical conclusion of #4 is that a particular re-expression of doctrine may be objectively true, properly understood, but that it may be expressed in a way such that it is easy or possible to take away the wrong meaning from it. It recognizes, in other words, that there is a difference between saying something correct (in, perhaps, Mandarin), and saying something correctly in Mandarin: “saying something correct” is the Magisterial bit, “saying something correctly” is the prudential bit, and while the Church cannot err in the former, I see no reason to believe the re-expressions themselves were necessarily the best possible ones, nor do I see any reason to believe that this failing would necessarily impugn the Church’s teaching authority.
We were promised that our teachings would ultimately be right, not that they would necessarily be understood in any particular way at any particular time by any particular group of people.
 Pope John XXIII, opening address at the Second Vatican Council, 11 October 1962.