You made my point. See what I wrote up above.
The story I told has nothing to do with what you wrote. For your info, the very first title the Church used for Mary was “Mother of God”. This was some time in the 3rd century at a council of Ephesus (present day Turkey). Even that far back, Mary was thought to be sinless. They did not make a big deal about it because it was generally accepted and the Catholic Church did not have to compete with another Christian faith.
What happened in 1854 was different. The Catholic Church had to make a formal statement as to its belief regarding the mother of Jesus. The Pope therefore declared ex-cathedra (from the chair of Peter, and therefore infallibly) that Mary was untouched by sin from the moment of her conception by her parents — it’s just that simple.