I may be incorrect in this and please correct me if I'm wrong. The first Vatican Council simply defined papal infallibility. However, it defined than when speaking "ex cathedra" the pope in inerrant in matters of dogma concerning faith and morals. Infallibility was bestowed by Christ to Peter (and his successors), and thus has existed since the Resurrection; it was not simply "invented" in 1870. Therefore, while the Immaculate Conception has been the only pronouncement "specified" as being infallible, many other articles of faith (the Virgin Birth, Christ's divinity, the Resurrection, the Trinity) are equally infallible.
Catholic theologians through the centuries have held the view that canonization is not invariably an act of papal infallibility and is certainly not a primary exercise thereof. St. Thomas Aquinas (Quodlibet 9.c.16) holds that the pope may err in this, as in other matters where his decision depends on the truth of human testimony. St. Robert Bellarmine holds that it is quite possible for the pope "to err in particular controversies of fact which depend chiefly on human information and testimony."
When and if the heirarchy of the Church returns to its senses, it can undo whatever unworthy "saints" John Paul the Silent elevates.
When a saint is declared by the Pope, it's considered to be infallible because it's actually the Holy Spirit who decides who's to become a saint and who isn't. If the Holy Spirit decides someone up for sainthood shouldn't get it (for whatever God's reason is -- not necessarily because they're not in Heaven), the process will be stopped somwhere along the line. That's how people end up with the titles of Servant of God, Venerable, and Blessed and never advance to Saint. The Holy Spirit stops it.