Brother, I just got done reading about the Iconoclast heresy. Are you trying to tell me that the "ancient" Church always and everywhere believed in the "worship" of icons? Or that the Holy Spirit was seen as a "theological" procession from the Father alone - and an "economical" procession from the Father and the Son? :) (Starting to figure out that Filioque thing, too!)
The latin Church believes in the "deposit of Faith" treating faith as a "seed" from which new things can grow that were not there when the Apostles, or the Church Fathers walked the earth. We do not see that any aspect fo the Faith known today was hidden from the knowledge of the Fathers and the Apostles, or that they didn't know it because they weren't around when the deposit-seed poduced new "leaves."
I would dare say that the Iconoclast heresy is just one example of many where the Church of the day interpreted what came before as the "teachings of the Apostles", although one could find numerous Patristic writings to the contrary, writings that superficially could and were used to "disprove" such use of "idols".
We believe that the Church is a living interpreter of the Apostles' teachings, even when given in seed form, as you say. The theologians of the day saw the worship of icons by the faithful as an expression of this "seed" teaching, and left it to the Council to officially proclaim what was already "proclaimed" always and everywhere. The Apostles gave a core of teachings that implied other teachings that developed from them - one being the utilization of icons and statues that was NOT idolatry, and the belief that praying for the sake of the dead was efficacious.
Sure, the theological definitions of "purgatory" were not set in stone by the faithful. Nor did people understand the theological implications of icons. But in both cases, I believe, we have enough evidence to show that the faithful practiced something that was not defined by theologians. In the case of icons, the practice of the faithful of prayers asking for intercession of saints through these icons was sufficient, among other things, for the settling of the icon heresy. In the case of Purgatory, the prayers for the sake of the dead provide all the evidence we need for the existence of "Purgatory" - there would be no point in praying for the sake of a person in heaven or hell. Its existence is even implied in the Old Testament writings of Maccabees, Scriptures to both our communities, so it must be an Apostolic teacing, if it still existed as a belief in Christian communities as noted by early Christian historians...
I believe in the Orthodox Church, an accepted Ecumenical Council has not "proclaimed" or "denied" the doctrine. But if they were to study the question (as we have been forced to by the Reformation), they would come to the conclusion of its existence - though with different ideas of the specifics. As in any other doctrine, it takes heresy to define the borders of what we believe. And we always go back to that "seed" found in the Apostolic teachings.
Regards
Your question is a heterogenious. But the answer is: Yes. Otherwise, the Church would not have known what was heresy and what was not.
Heresies simply forced the Church to spell out what it was that the Church disagreed with and why. But the knowledge of the "why" was there all along. Thus, when Aries started to teach that Chrust was a "lesser" God than the Father, that He was a "creature," the Church knew that was wrong.
The Latins did not begin to use the filioque (and yes you are getting sclose) until the Arian heresy gave reason to compati it with filioque. Until that time the Spanish priests recited the Creed just like everyone else. The filioque was used to convince the Arians that Christ was co-substantial with the Father and not because the Creed was "incomplet" or "wrong."
As for iconoclast heresy, the early documentation shows that the Church as far back to the Apostolic times used pictures of holy people, and that none of the Cappadocian Fathers found it objectionable as neither did any of the Church Fathers before or after them.
St. John the Damascene defeated iconoclastic movement using the existing knowledge of faith and not adding to it. The Pope resisted the iconoclasts of the 8th century for the same reasons: there was no evidence in the Tradition that any of the Fathers and Patriarchs found anything wrong with the use of the icons.