When is the RC denomination going to finally declare itself full?
Hey House (i like the sound of that

),
I understand your concern. My reply is just what I see as the Church understanding of your arguement.
It always has. Defining the deposit of faith is not the same as “gaining new faith” or “receiving a new Truth”
Your best arguement is probably the Marian Dogmas.
CCC:
84 The apostles entrusted the “Sacred deposit” of the faith (the depositum fidei),45 contained in Sacred Scripture and Tradition, to the whole of the Church. “By adhering to [this heritage] the entire holy people, united to its pastors, remains always faithful to the teaching of the apostles, to the brotherhood, to the breaking of bread and the prayers. So, in maintaining, practicing, and professing the faith that has been handed on, there should be a remarkable harmony between the bishops and the faithful.”46 (857, 871, 2033)
The Magisterium of the Church
85 “The task of giving an authentic interpretation of the Word of God, whether in its written form or in the form of Tradition, has been entrusted to the living, teaching office of the Church alone. Its authority in this matter is exercised in the name of Jesus Christ.”47 This means that the task of interpretation has been entrusted to the bishops in communion with the successor of Peter, the Bishop of Rome. (888-892, 2032-2040)
86 “Yet this Magisterium is not superior to the Word of God, but is its servant. It teaches only what has been handed on to it. At the divine command and with the help of the Holy Spirit, it listens to this devotedly, guards it with dedication, and expounds it faithfully.
All that it proposes for belief as being divinely revealed is drawn from this single deposit of faith.”48 (688)The fullness of Truth has always existed in the Catholic Church because of His Eucharist. Interpreting the life of Christ is given first to Peter and the Apostles.
1324 The Eucharist is “the source and summit of the Christian life.”136 “The other sacraments, and indeed all ecclesiastical ministries and works of the apostolate, are bound up with the Eucharist and are oriented toward it. For in the blessed Eucharist is contained the whole spiritual good of the Church, namely Christ himself, our Pasch.”
Colossians 2:2-3 (RSVCE)
“That their hearts may be encouraged as they are knit together in love, to have all the riches of assured understanding and the knowledge of God’s mystery, of Christ, in whom are hid all the treasures of wisdom and knowledge.”