This had been done only two times in the entire history of the Catholic Church.
With all due respect, the Church has used her infallibility many more times than the definitions of the Immaculate Conception and the Assumption. If you need some examples, I'd be happy to send some in your direction. You could start with the Canons and Decrees of Trent and Vatican I, the definitions of Niceae, Constantinople, Chalcedon, Ephesus, Lyons, Florence, etc. Then there are the infallible definitions of Benedict XII on the Beatific Vision, of Boniface VIII on the powers of the Pope and the Church, of Pius XII on the matter of Holy Orders, of John Paul II on the evils of abortion and euthanasia and the inability of women to be ordained, of Pius X and Benedict XIV on the damnation of the ignorant, of Leo XIII on the invalidity of the Anglican Ordinal, just to name a few. To follow up this, there are all the papal canonization decrees, the lists of condemned errors (such as Pius IX's Syllabus, or the multiple condemndations of the Jansenists and Laxists). Need I go on?