The sede sects are far worse in EENS, for many of them reject the plain sense of the Athanasian Creed. Implicit Baptism of Desire is Catholic Doctrine, it is taught even by His Holiness Pope St. Pius X in his Catechism. The idea of salvation by implicit faith in Christ is a different idea and an erroneous one. The Magisterium of the Catholic Church, in the Catechism of the Catholic Church, favors explicit faith.
Here's the state of the question on explicit and implicit faith in Christ, per 3 pre-Vatican II authorities, and the teaching of St. Alphonsus, who cites St. Thomas and others.
Fr. Sylvester Hunter, in Outlines of Dogmatic Theology (1895) writes: "Regarding the points on which explicit knowledge is required as the indispensable means of justification, this certainly extends to the belief that God exists and that He shows Himself the Rewarder of them that seek Him. This amount of belief is declared by St. Paul to be essential, if any one will please God. (Hebrews 11:6) ... So far there is universal agreement, and in fact the necessity that we have stated is not open to doubt, for Pope Innocent XI condemned the assertion that explicit belief that God rewards is not necessary (prop. 22; Denz. 1039). There is a controversy whether St. Paul, in the passage quoted, intended to mention all that is necessary, or whether explicit belief in the Trinity and Incarnation is required ... many followers of the Thomist school hold that it has been necessary since the revelation was brought by Christ ... These found their opinion upon the language of Scripture, which frequently speaks of faith in Christ as the essential condition of salvation; and to believe in Christ means to believe that He is God and Man."
Fr. Michael Mueller, CSSR, citing St. Alphonsus and other authorities: "Some theologians hold that the belief of the two other articles - the Incarnation of the Son of God, and the Trinity of Persons - is strictly commanded but not necessary, as a means without which salvation is impossible; so that a person inculpably ignorant of them may be saved. But according to the more common and truer opinion, the explicit belief of these articles is necessary as a means without which no adult can be saved.”
Msgr. Joseph Clifford Fenton, writing during the reign of Pope Ven. Pius XII: "most theologians teach that the minimum explicit content of supernatural and salvific faith includes, not only the truths of God’s existence and of His action as the Rewarder of good and the Punisher of evil, but also the mysteries of the Blessed Trinity and the Incarnation"
In Theologia Moralis, Lib.III, Cap 1, Q. 2 St. Alphonsus wrote against implicit faith: "They [the proponents of salvation by implicit faith in Christ] respond that even though all the Scriptures and Holy Fathers’ testimonies oppose this opinion, their opinion [the "opinion" of the Scriptures, as confirmed by the exegesis of the unanimous "opinion" of the Fathers] is more easily explained by necessity of precept, or because ordinarily almost none are saved without explicit faith in the mysteries, because after the promulgation of the gospel almost no one labors out of invincible ignorance."
St. Alphonsus also answers the most common objection to it, citing St. Thomas "What about those who are too difficult for God to reach?" - "Thus, then, according to the Angelic Doctor, God, at least remotely, gives to infidels [non-Christians], who have the use of reason, sufficient grace to obtain salvation, and this grace consists in a certain instruction of the mind, and in a movement of the will, to observe the natural law; and if the infidel cooperates with this movement, observing the precepts of the law of nature, and abstaining from grievous sins, he will certainly receive, through the merits of Jesus Christ, the grace proximately sufficient to embrace the Faith, and save his soul" Thus, anyone who co-operates with God in observing natural law will, by degrees, come to the knowledge of Christ. God's Providence will not fail in this, whether it is sending an Angel, a Preacher, or Interior Illumination, say Sts. Thomas and Alphonsus
If we take the Creed of St. Athanasius in its most plain sense, "Whoever wishes to be saved must above all hold the Catholic Faith ... the Catholic Faith is this, that we worship God in Trinity and Trinity in unity ... which faith except a man hold firmly and faithfully, without a doubt he will perish in eternity.. he therefore that will be saved, let him think thus on the Trinity. Further it is necessary for eternal salvation that he also believes in the Incarnation of Our Lord Jesus Christ", Tradition also favors explicit over implicit faith.
Notice how beautifully the Magisterium teaches, "848 "Although in ways known to himself God can lead those who, through no fault of their own, are ignorant of the Gospel, to that faith without which it is impossible to please him, the Church still has the obligation and also the sacred right to evangelize all men."338. This means that those who are invincible ignorance, can be saved, but not as they are; they will be led by God, in a way known to Him, to that faith without which it is impossible to please Him, which in light of CCC 161, was earlier declared to be faith in Jesus Christ, for it said faith in Jesus Christ and the One Who sent Him for our Salvation is necessary for obtaining that Salvation.
For the sede and other separated sects to return to the Catholic Church, full assent of mind and will to the Catechism is requisite.