From what I understand, the Church's stance on papal infallibility only applies to faith and morals.
To fulfill this service, Christ endowed the Church's shepherds with the charism of infallibility in matters of faith and morals. (Catechism of the Catholic Church #891
http://www.scborromeo.org/ccc/p123a9p4.htm
ex-cathedra
The currently used definition comes from First Vatican Council (1869-1870):
"When the Roman Pontiff speaks ex cathedra...as the pastor and teacher of all Christians [and] defines a doctrine of faith and morals that must be held by the Universal Church, he is empowered, through the divine assistance promised him in blessed Peter, with the infallibility with which the Divine Redeemer willed to endow his Church."
Here is where it gets interesting. The doctrine of infallibility relies on one of the cornerstones of Catholic dogma: that of petrine supremacy of the pope, and his authority as the ruling agent who decides what is accepted as formal beliefs in the Roman Catholic Church. The use of this power is referred to as speaking ex cathedra. The solemn declaration of papal infallibility by Vatican I took place on 18 July 1870.
https://en.wikipedia.org/wiki/Papal_infallibility
On 18 November 1302, Pope Boniface VIII issued the Papal bull Unam sanctam[a] which some historians consider one of the most extreme statements of Papal spiritual supremacy ever made. The Bull lays down dogmatic propositions on the unity of the Catholic Church,
the necessity of belonging to it for eternal salvation, the position of the pope as supreme head of the Church, and the duty thence arising of submission to the pope in order to belong to the Church and thus to attain salvation. The pope further emphasizes the higher position of the spiritual in comparison with the secular order.
In recent times, the Church has recognized that its teaching about the necessity of the Catholic Church for salvation has been widely misunderstood, so it has "re-formulated" this teaching in a positive way. Here is how the Catechism of the Catholic Church begins to address this topic: "How are we to understand this affirmation, often repeated by the Church Fathers? Reformulated positively, it means that all salvation comes from Christ the Head through the Church which is his Body" (CCC 846).
http://www.catholic.com/magazine/articles/what-no-salvation-outside-the-church-means
For the Jews
Vatican City, Dec 11, 2015 / 06:01 am (CNA/EWTN News).- Though it “is and remains an unfathomable divine mystery,” Jews can participate in salvation without confessing Christ explicitly, a Vatican committee said in a document released on Thursday.
http://www.catholicnewsagency.com/n...ion-of-salvation-for-the-jewish-people-65742/
For the Muslims
Lumen Gentium, (DOGMATIC CONSTITUTION ON THE CHURCH), POPE PAUL VI, November 21, 1964, section 16:
16. ... But the plan of salvation also includes those who acknowledge the Creator. In the first place amongst these there are the Mohamedans, who, professing to hold the faith of Abraham, along with us adore the one and merciful God, who on the last day will judge mankind.
NOSTRA AETATE, (DECLARATION ON THE RELATION OF THE CHURCH TO NON-CHRISTIAN RELIGIONS), POPE PAUL VI, October 28, 1965, section 3:
3. The Church regards with esteem also the Moslems. They adore the one God, living and subsisting in Himself; merciful and all-powerful, the Creator of heaven and earth,(5) who has spoken to men; they take pains to submit wholeheartedly to even His inscrutable decrees, just as Abraham, with whom the faith of Islam takes pleasure in linking itself, submitted to God. Though they do not acknowledge Jesus as God, they revere Him as a prophet. They also honor Mary, His virgin Mother; at times they even call on her with devotion. In addition, they await the day of judgment when God will render their deserts to all those who have been raised up from the dead. Finally, they value the moral life and worship God especially through prayer, almsgiving and fasting.
So, according to the Catholic Catechism, Muslims and Jews will be saved despite their rejection of Jesus Christ as the Savior (839-841), and the ignorant can be saved despite their ignorance of Jesus Christ (847), but Protestant Christians who are dedicated Christians that know and accept Jesus Christ as their Savior, yet stubbornly and "knowingly" refuse to become Catholics, are heretics and cannot possibly be saved!
So from all this I have come to see the even papal infallibility can have an "except" added later as needed.