Neither Rerum Novarum, nor Centisimus Annos, nor any of Pope Francis' teachings, are protected by Papal infallibility. It's debatable whether something which strayed far from moral principles into the specifics of their practical applications even *could* be protected by Papal infallibility.
>what is protected by Papal infallibility?
This goes to the definition of “infallible” to Catholics. To non-Catholics, a better word might be “presumption.”
There are degrees of infallible. The Pope speaking spontaneously is to be given presumption. Hence, there is some weight to Pope Benedict XVI’s spontaneous remark that Christianity is not a political nor an economic system.
The Pope in issuing this pastoral letter is to be given a greater degree of presumption.
The Pope in issuing encyclical even more so.
And, the Pope issuing an encyclical in conjunction with the bishops of the Church would be the highest level of presumption. Don’t quote me on this, but I think there have only been seven in two thousand years of Church history. They concern such matters as Christ’s nature as truly God and truly Man (which is not to say that Christ has two separate natures).
The bishops of the United States, when they issue a pastoral letter, deserve a certain presumption. But, I’ll just say with regard to economics, these pastoral letters have been as embarrassing as Pope Francis’ exhortation.
The Doctors of the church also deserve a certain presumption. Their teachings are said to be relatively free of error. Hence, we can have some confidence in St. Theresa’s great teaching that our little things are acceptable to God.
If I might return to Pope Benedict XVI, I did very much enjoy his spontaneous remark, when asked by the crowd upon being elected Pope to instantly declare John Paul II a saint, “Are we not all saints?” Very Baptist of him.