Where is that distinction when each individual claims his or her own authority in determining and interpreting scripture?
Scripture teaches its own sufficiency as God’s revelation, and it possesses the innate ability to communicate clearly and understandably the necessary truths for faith and morals for every Christian. Irenaeus said:
Since, therefore, the entire Scriptures, the prophets, and the Gospels, can be clearly, unambiguously, and harmoniously understood by all, although all do not believe them; and since they proclaim that one only God, to the exclusion of all others, formed all things by His word, whether visible or invisible, heavenly or earthly, in the water or under the earth, as I have shown from the very words of Scripture; and since the very system of creation to which we belong testifies, by what falls under our notice, that one Being made and governs it—those persons will seem truly foolish who blind their eyes to such a clear demonstration, and will not behold the light of the announcement [made to them]; but they put fetters upon themselves, and every one of them imagines, by means of their obscure interpretations of the parables, that he has found out a God of his own. (ANF, Vol. I, Irenaeus, Against Heresies II.27.2)
He also stated:
To which course many nations of those barbarians who believe in Christ do assent, having salvation written in their hearts by the Spirit, without paper or ink, and, carefully preserving the ancient tradition, believing in one God, the Creator of heaven and earth, and all things therein, by means of Christ Jesus, the Son of God; who, because of His surpassing love towards His creation, condescended to be born of the virgin, He Himself uniting man through Himself to God, and having suffered under Pontius Pilate, and rising again, and having been received up in splendor, shall come in glory, the Savior of those who are saved, and the Judge of those who are judged, and sending into eternal fire those who transform the truth, and despise His Father and His advent. Those who, in the absence of written documents, have believed this faith, are barbarians, so far as regards our language; but as regards doctrine, manner, and tenor of life, they are, because of faith, very wise indeed; and they do please God, ordering their conversation in all righteousness, chastity, and wisdom. If any one were to preach to these men the inventions of the heretics, speaking to them in their own language, they would at once stop their ears, and flee as far off as possible, not enduring even to listen to the blasphemous address. Thus, by means of that ancient tradition of the apostles, they do not suffer their mind to conceive anything of the [doctrines suggested by the] portentous language of these teachers, among whom neither Church nor doctrine has ever been established (ANF, Vol. I, Irenaeus, Against Heresies III.4.2).
So, it is not a matter of "each individual claims his or her own authority in determining and interpreting Scripture", but of those whose hearts are open to the leading of the Holy Spirit in illuminating the truths of God set forth in Holy Scripture that he clearly reveals EVEN to those who have not read them.
Catholics are no different. When they decide to accept the RCC interpretation of Scripture, they are accepting it as their own. Their own personal interpretation happens to agree with the RCC when they accept the RCC one.
But either way, it is still an individual choice to accept a personal interpretation of Scripture. Just because any one Catholics happens to agree with any other one Catholics is irrelevant.
EVERY person's decision is a personal interpretation of Scripture. It just matters whose it is, whether it's the *church's* or your own.