Which is selectively done, as such things as the IC lack unanimous consent of the fathers, and the Assumption lacks weight of early testimony , and in other things Rome differs with the EOs on what Tradition teaches, even as in the case of universal papal jurisdiction and papal infallibility, among other things.
The reading that since the fullness of grace preceded the arrival of the angel...
That this grace was perpetual sinlessness is presumed, versus that grace being that this evidently holy Spirit-filled soul had "found grace with God" as the text states, (Lk. 1:30) in being chosen to be the God-bearer.
God has the power to raise any kind of Mary He wants for His own mother, and probably would not want a sinner in that role
One could argue that God would not want the instruments out of whom flowed God-breathed Scripture to be sinners either, or Mary's parents, etc.
But doctrine is not based on what God may or could have done, or silence, but what the evidence testifies He did do. Lacking that, all that is warranted is speculation. Notable exceptions to the norm (excess fingers, long age, celibacy, absence of parents, sinlessness, etc) are characteristically provided in Scripture, even of lesser characters, and the sinlessness of Christ is stated at least thrice. Marian lifelong sinlessness and virginity are not, but are read into the text based upon the fallacious idea of necessity, or possibility.
In contrast to all that attributed to her, the mention of Mary is relatively marginal in Scripture, while the Holy Spirit gives far more description of Paul's sacrificial labor of love in birthing spiritual children and churches, and working toward their maturity. And the Holy Spirit never manifestly attributes sin to him after his conversion, but to say that he was sinless would be presumptuous.
The Church does not do what the Protestants do, read the scripture and in it find the doctrine.
That is rare admission, as too many RCs try to argue as if they were evangelicals in trying to wrest support for Rome's traditions as if their veracity rested upon the weight of Scriptural warrant.
But by making her amorphous oral tradition equal with Scripture, selectively channeling ancient stories into binding doctrines, then Catholicism (sometimes in conflict), has perpetuated mere traditions that developed over time.
The oral "traditions" Paul wrote of were not that of ancient tales, but known contemporary preaching which we rightfully can expect were subsequently written, as is seen elsewhere with revelation called "the word of God/the Lord."
Details hitherto unknown as recorded could be revealed (cf. 2Tim. 3:8) but which we know by Scripture, which is the assured word of God and supreme standard for testing and establishing Truth claims. Making the church autocratically supreme is contrary to its basis of establishment, that of Scriptural substantiation in word and in power, and making her oral tradition as equal with Scripture is essentially adding to the canon.
'presumption and assumption are closely related.
I've experienced what it is to assume....