By the way, NFP was not new with Humae Vitae, the Church has always upheld it as a valid means of family planning:
From an article in “This Rock” (the whole article is worth reading):
catholic.com/thisrock/2005/0502fea2.asp
The first time Rome spoke on the matter was 1853, when the Sacred Penitentiary answered a
dubium (a formal request for an official clarification) submitted by the bishop of Amiens, France. He asked, “Should those spouses be reprehended who make use of marriage only on those days when (in the opinion of some doctors) conception is impossible?” The reply was: “After mature examination, we have decided that such spouses should not be disturbed [or disquieted], provided they do nothing that impedes generation” (quoted in J. Montánchez,
Teología Moral 654, my translation). By the expression “impedes generation,” it is obvious the Vatican meant the use of onanism (or
coitus interruptus, now popularly called “withdrawal”), condoms, etc. Otherwise the reply would be self-contradictory.
The next time the issue was raised was in 1880, when the Sacred Penitentiary issued a more general response . The precise question posed was this: “Whether it is licit to make use of marriage only on those days when it is more difficult for conception to occur?” The response was: “Spouses using the aforesaid method are not to be disturbed; and a confessor may, with due caution, suggest this proposal to spouses, if his other attempts to lead them away from the detestable crime of onanism have proved fruitless.” (This decision was published in
Nouvelle Revue Théologique 13 [1881]: 459–460 and in
Analecta Iuris Pontificii 22 [1883], 249.)
One could not ask for a more obvious and explicit proof that more than eighty years before Vatican II, Rome saw a great moral difference between NFP (as we now call it) and contraceptive methods, which Catholic moralists then referred to as
onanism.
This was the doctrine and pastoral practice that all priests learned in seminary from the mid-nineteenth century onward. Before Pius XI was elected, Blessed Pius IX, Leo XIII, St. Pius X, and Benedict XV all clearly approved of this status quo established by their own Sacred Penitentiary and never showed the slightest inclination to reverse its decisions of 1853 and 1880.