Baltimore Catechism No.3
A Catechism of Christian Doctrine prepared and enjoined by order of the Third Plenary Council of Baltimore
IMPRIMATURS:
Archbishop John McCloskey of New York 1885
Archbishop Gibbons Baltimore 1885
Archbishop Michael Augustine N.Y. 1901
Archbishop Patrick Hayes N.Y. 1921
NIHIL OBSTATS:
Rev. Remigius LaFort, Censor Librorum 1901
Arthur Scanlan, Censor Librorum 1921

Q. 510. Is it ever possible for one to be saved who does not know the Catholic Church to be the true Church?
A. It is possible for one to be saved who does not know the Catholic Church to be the true Church, provided that person (I) has been validly baptized; (2) firmly believes the religion he professes and practices to be the true religion, and (3) dies without the guilt of mortal sin on his soul.

Q. 511. Why do we say it is only possible for a person to be saved who does not know the Catholic Church to be the true Church?
A. We say it is only possible for a person to be saved who does not know the Catholic Church to be the true Church, because the necessary conditions are not often found, especially that of dying in a state of grace without making use of the Sacrament of Penance.

Q. 512. How are such persons said to belong to the Church?
A. Such persons are said to belong to the "soul of the church"; that is, they are really members of the Church without knowing it. Those who share in its Sacraments and worship are said to belong to the body or visible part of the Church.

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The fallible American Bishops approved this one but it is incorrect to say they are members of the Church.  They are not.  The Feeneyites rightly see the error here and figure the entire theology contained in approved Catechisms on Salvation is wrong.  This question (512) assumes one must really be a member of the Catholic Church in order for salvation to be possible.  So to square the round peg they go with "member" of the "soul" of the Church as if there are two different Church's body and soul.  

The Feeneyites are correct when they claim imprimatured and Nihil Obstated books can err and this is a prime example.  

Father Fenton thoroughly explains how it came about the error in this issue was taught by respected theologians.  It would be comical were it not so serious.