Pre-Responding to the "Immaculate" => "Immaculate Conception" Argument

It's hard to know exactly how Mr. Albrecht intends to defend against the fact that so many popes taught contrary to the dogma of the immaculate conception before its definition in the 19th century. In a previous post, I discussed the specific arguments I expect to hear from Albrecht about certain contra-IC quotations, but Albrecht claimed that he was sitting on a pile of quotations on the other side. What could those be?

My best guess (based on Mr. Albrecht's arguments in other debates on the subject) is that they include quotations like these:

Leo I, Sermon 31 (link)
"After celebrating but lately the day on which immaculate virginity brought forth the Saviour of mankind, ..."

7th Ecumenical Council, Decree (link)
"With the Fathers of this synod we confess that he who was incarnate of the immaculate Mother of God and Ever-Virgin Mary has two natures, recognizing him as perfect God and perfect man, as also the Council of Chalcedon has promulgated, ..."

6th Ecumenical Council (link)
- Letter of Agatho
"Moreover we confess that one of the same holy consubstantial Trinity, God the Word, who was begotten of the Father before the worlds, in the last days of the world for us and for our salvation came down from heaven, and was incarnate of the Holy Ghost, and of our Lady, the holy, immaculate, ever-virgin and glorious Mary, truly and properly the Mother of God, that is to say according to the flesh which was born of her; ..."

- Prosphoneticus to the Emperor
"For as the Word, he is consubstantial and eternal with God his father; but as taking flesh of the immaculate Virgin Mary, the Mother of God, he is perfect man, consubstantial with us and made in time."

These and many other writings describe Mary and/or her virginity as "immaculate." A modern reader will be tempted to automatically associate the term "immaculate" with the dogma of the "immaculate conception." This is particularly tempting for Protestants, who reject the idea that Mary was sinless, and consequently would affirm that her virginity was immaculate at the incarnation, and that she had been justified by faith, but not that she was otherwise sinless. Tempting though it may be, it's an equivocation fallacy.

State vs. Event
To avoid this equivocation fallacy, note well the difference between a state and an event. The state of being sinless is one thing, and how a person became sinless is another thing. For example, there is a view of baptismal regeneration that suggests that when a person is baptized, they are made pure from original sin and all preceding actual sins. Likewise, the doctrine of justification by faith alone also teaches that in justification we are rendered guiltless. Without getting into the important distinctions between baptismal regeneration (defined that way) and justification by faith alone, the point is that a person is in some sense sinless in both cases. Likewise, both Roman Catholics and Protestants agree that those in heaven are sinless.

So, even if Scripture had said that Mary was sinless (a state) at Jesus' conception, that would not necessarily tell us how she became that way (an event). Scripture does not speak of Mary in that way, while some in the Patristic era and many in the medieval era definitely did speak of Mary as sinless. How could she be sinless if she was not immaculately conceived? She could have been purified from sin rather than being preserved from sin.

What about other possible arguments? It's hard to say. I recall Mr. Albrecht taking the position that Leo the Great exegeted Genesis 3:15 in a way that represents Mary as the New Eve, or something to that effect. Those kind of arguments should readily be seen to be a rabbit trail.

-TurretinFan