First off, I don’t appreciate your implying that I am some amateur hack who, as a convert, does not know the faith. I am aware that not all doctrines are dogmas and that all dogmas are doctrines. The CDF commentary was talking about both dogmas and doctrines. Go back and read it again.
Second, I am very familiar with Ott’s “Fundamentals of Catholic Dogma.” Not only is it in “practically every Roman Catholic seminary,” but it is also in my own personal library. Thank you for reminding me of it!
On pg. 9-10, in discussion of the Theological Grades of Certainty, it expressly proves you wrong. Nowhere does it say that not all doctrines require the assent of faith, rather it says:
“With regard to the doctrinal teaching of the Church it must be well noted that not all the assertions of the Teaching Authority of the Church on questions of Faith and morals are infallible and consequently irrevocable…Nevertheless normally they are to be accepted with an inner assent which is based on the high supernatural authority of the Holy See.”
Now, owning Ott’s book (which is subtitled: “A One-Volume Encyclopedia of the Doctrines of the Catholic Church, showing their sources in Scripture and Tradition and their definitions by Popes and Councils), I decided to look in it for “Co-redemptrix.” And since it is indeed a doctrine of the Church, on page 211 (which is Chapter 3 of the section entitled, “The Mother of the Redeemer”) I find the heading “Mary’s Co-operation in the Work of Redemption.” On the next pages (212-213) I find what is quoted below:
“Mary’s co-operation in the Redemption:
The title Corredemptrix=Coredemptress, which has been current since the fifteenth century, and which also appears in some official Church documents under Pius X (cf. D 1978a), must not be conceived in the sense of an equation of the efficacy of Mary with the redemptive activity of Christ, the Sole Redeemer of humanity (1 Tim 2.5). As she herself required redemption and in fact was redeemed by Christ, she could not of herself merit the grace of the redemption of humanity in accordance with the principle: Principium meriti non cadit sub eodem merito. (The author of an act of merit cannot be a recipient of the same act of merit.) Her co-operation in the objective redemption is an indirect, remote co-operation, and derives from this that she voluntarily devoted her whole life to the service of the Redeemer, and under the Cross, suffered and sacrificed with Him. As Pope Pius XII says in the Encyclical ‘Mystici Corporis’ (1943), she ‘offered Him on Golgotha to the Eternal Father together with the holocaust of her maternal rights and her motherly love like a new Eve for all children of Adam’ (D 2291). As ‘The New Eve’ she is, as the same Pope declares, in the Apostolic Constitution ‘Munificentissimus Deus’ (1950) ‘the sublime associate of our Redeemer’ (alma Redemptoris nostri social (cf. Gen 3.12). Cf. D. 3031: generoso Divini Redemptoris social.
Christ alone truly offered the sacrifice of atonement on the Cross; Mary merely gave Him moral support in this action. Thus Mary is not entitled to the title ‘Priest’ (sacerdos). Indeed this is expressly laid down by the Holy Office (1916, 1927). Christ, as the Church teaches, ‘conquered the enemy of the human race alone (solus)’ (D 711); in the same way, He alone acquired the grace of Redemption for the whole human race, including Mary. The words of Luke I, 38: ‘Behold the handmaid of the Lord,’ imply Mary’s mediate, remote co-operation in the Redemption. St. Ambrose expressly teaches: ‘Christ’s Passion did not require any support’ (De inst. Virg. 7). In the power of the grace of Redemption merited by Christ, Mary, by her spiritual entering into the sacrifice of her Divine Son for men, made atonement for the sins of men, and (de congruo) merited the application of the redemptive grace of Christ. In this manner she co-operates in the subjective redemption of mankind.
The statement of Pope Pius X in the Encyclical ‘Ad diem illum’ (1904): (Beata Virgo) de congruo, ut aiunt, promeret nobis, quae Christus de condign promeruit (D 1978a) (The Blessed Virgin merits for us de congruo what Christ merited de condign) is, as the present tense ‘promeret’ shows, not intended to be taken as referring to the historical objective Redemption, which occurred once and for all, but to her ever-present, intercessory co-operation in the subjective redemption.”
Now, I took the liberty of looking up the Denzinger quote (D 1978a) from his “The Sources of Catholic Dogma” which Ott references in the beginning of the above quote. There you will find this:
“In the decree of the S.C. of the Holy Office (section on Indulgences), “Sunt quos amor,” June 26, 1913 (AAS 5  364), he [Pius XI] praises the custom of adding to the name of Jesus the name of “His Mother, our coredemptor, the blessed Mary”; cf. also the prayer enriched by the Holy Office with an indulgence, in which the Blessed Virgin Mary is called “coredemptress of the human race” (Jan. 22, 1914; AAS 6  108).”
Also, you said that “Co-redemptrix” is not taught in Scripture, the Fathers, or the Magisterium. Just because the title is not explicitly named, does not mean it is not taught. The doctrine of Mary’s coredemption is actually quite Biblical, and can definitely be found in the Fathers and the Magisterium (as evidenced by Taylor’s quote from Irenaeus in this post).
So you see, the title of “Co-redemptrix” applied to Mary is not only fitting, it is a doctrine of the Church. Do you still wish to deny this doctrine in the face of all this evidence?
Ad Jesum per Mariam,