Let us take a brief look at the confusion associated with the IC theology prior to Pius IX elevating it to a doctrine of the post schism Latin Church.
The question concerning the Immaculate Conception of the Blessed Virgin Mary had been agitated with great warmth in the university of Paris, when both the university and the bishop, in 1387, condemned certain propositions of John de Montesano, a Dominican, in which this privilege was denied. The Council of Basle, in 1439 (Sess. 36), declared the belief of her Immaculate Conception to be conformable to the doctrine and devotion of the church, to the Catholic faith, right reason, and the holy scriptures, and to be held by all Catholics. But this council was at that time a schismatical assembly, nor could its decree be of force. It was, nevertheless, received by a provincial council held at Avignon in 1457, and by the university of Paris. When some gave scandal by warmly contesting the Immaculate Conception, this famous university passed a decree in 1497, in which it was enacted, that no one should be admitted in it to the degree of doctor of divinity who did not bind himself by oath to defend this point. (See Spondan, Contin. Baron. Ad an. 1497; Bulaeus, Hist. Universit. Paris, t. 5, p. 815; Fleury, cont. t. 24, p. 336; Frassen, t. 8, p. 227). The council of Trent declared, in the decree concerning original sin, that it was not its intention to include in it the Immaculate Virgin, the Mother of God, and ordered the decree of Sixtus IV, relating to this point, to be observed. That pope, in 1476, granted certain indulgences to those who assisted at the office and mass on the feast of her Conception; and, in 1483, by another constitution, forbade anyone to censure this festival, or to condemn the opinion which asserted the Virgin Mary’s Immaculate Conception. St. Pius V, by his bull in 1570, forbade either the opinion which affirmed, or that which denied it, to be censured. Paul V, in 1616, reiterated the same prohibition, and, in 1617, forbade anyone to affirm in sermons, theses, or other like public acts, that the Blessed Virgin Mary was conceived in original sin. Gregory XV, in 1622, forbade anyone to affirm this, even in private disputations, except those to whom the holy see gives a special license to do it, which he granted to the Dominicans, provided they do it privately, and only among themselves [emphasis added]; but he ordered that, in the office or mass of this festival, no other title than simply that of the Conception should be used. Alexander VII, in 1671, declared that the devotion of honoring the Immaculate Conception of the Virgin Mary is pious; yet prohibits censuring those who do not believe her Conception immaculate. Philip III of Spain, demanded of Paul V, and Philip IV, of Gregory XV, a definition of this question, but could obtain nothing more than the foregoing bulls. (See Luke Wadding, the learned Irish Franciscan, who lived some time in Spain, and died at Rome in 1655, De Legatione Philippi III et Philippi IV ad Paulum V et Greg. XV, pro definienda Controversia de Conceptione Virginis). In the latest edition of the Roman Index, a certain little office of the Immaculate Conception is condemned; but this censure is not to be extended to other such little offices. In the prayers themselves it is called the Conception of the Immaculate Virgin, which phrase is ambiguous, and may be understood to imply only that she was spotless from all actual sin, and was cleansed from original sin before she was born, in which all Catholics agree. Benedict XIII granted to the subjects of Austria, and the empire a weekly office of the Immaculate Conception on every Saturday; but the epithet Immaculate Conception occurs not in any of the prayers, but only in the title of the office.
(Butler, op. cit. vol. IV p. 493)
