I’d like to compare two of the commenters. Lutheran minister Rev. McCain takes more or less the view that Trent must be understood the way Trent understood what they stated. Roman apologist Bryan Cross says, in essence, that changes in historical condition effect the way Trent is understood. It comes down to interpreters of the infallible interpreter, on the one hand. I’ve always enjoyed the fact that the infallible interpreter must needs be fallibly interpreted.
On the other hand, the basic underlying issue, is authority. Someone probably reading my above synopsis of McCain and Cross may reply: Isn’t that the same problem with interpreting the Bible? Is it to be understood correctly based on it’s original audience, or is it something that applies differently and is understood differently in later ages? That of course, is a greatly debated question. Here though the underlying question is not how to interpret Rome correctly, or who interprets Rome correctly. The question is, is Rome really the infallible voice of God? That’s what all these Roman Catholic issues come down to, don’t they?
Mr. Cross is simply arguing according to his basic presuppositions. In his worldview, it all works out (it has to). Mentioning Küng or arguing like Rev. McCain did probably won’t dent the Romanist armor Mr. Cross has put on, that is, he won’t feel it. For Mr. Cross, since Rome is the infallible voice of God, any sort of argument that she isn’t will be subject to some sort of counter-reply, because Trent was… infallible. That’s assumed. There has to be a reply and a way to understand the situation because... Trent is assumed to be an infallible council. This reminds me of how Mr. Michuta argued that the blatant historical errors in the apocrypha weren’t errors because the apocrypha is God’s infallible word. If Roman apologists really believe their church has the infallible voice of God, it's most likely no amount of proof otherwise will change their minds.
Addendum: In regard to interpreting Romanism:
“The question before us is this: Is the Council of Trent’s teaching on justification the church’s final word? Emphatically not. Rome has developed its doctrine of justification, and it will doubtless continue to do so. None of the ecumenical councils, not even Chalcedon or Nicea, is terminal in the sense that it ends all possible development. They are not terminal, but they are decisive. Rome can indeed develop the views expressed at Trent. What it cannot do without radically altering its view of itself is repudiate or ‘correct’ Trent. Those who look for such a repudiation, or who think they have already found it, are whistling in the dark.” [Sproul, R.C., Faith Alone : The Evangelical Doctrine of Justification (Grand Rapids: Baker Books, 1995) pp.120-121]
There was a great ambiguity as to what exactly “justification” was even at Trent, documented by Alister McGrath: “The Council of Trent was faced with a group of formidable problems as it assembled to debate the question of justification in June 1546. The medieval period had witnessed the emergence of a number of quite distinct schools of thought on justification, clearly incompatible at points, all of which could lay claim to represent the teaching of the Catholic church.” [Alister McGrath, Iustitia Dei: A History of the Christian Doctrine of Justification (New York: Cambridge University Press, 259)]. McGrath goes on to point out “…[T]here was considerable disagreement in the immediate post-Tridentine period concerning the precise interpretation of the decretum de iustificatione” [ibid. 268]. In other words, even after Trent made its decree on Justification, Catholics were confused as to how to interpret it.