On November 1, 1950, Pope Pius XII solemnly declared:
By the authority of our Lord Jesus Christ, of the Blessed Apostles Peter and Paul, and by our own authority, we pronounce, declare, and define it to be a divinely revealed dogma: that the Immaculate Mother of God, the ever Virgin Mary, having completed the course of her earthly life, was assumed body and soul into heavenly glory
Roman Catholic theologians consider this declaration by Pius XII to be an ex cathedra use of Papal Infallibility.Although Pope Pius XII deliberately left open the question of whether Mary died before her Assumption, the more common teaching of the early Fathers is that she did.
In his August 15, 2004 homily given at Lourdes, Pope John Paul II quoted John 14:3 as one of the scriptural bases for understanding the dogma of the Assumption of Mary. In this verse, Jesus tells his disciples at the Last Supper, “If I go and prepare a place for you, I will come again, and will receive you to myself; that where I am, you may be there also.” According to Catholic theology, Mary is the pledge of the fulfillment of Christ’s promise.
12:1 of the Bible is pretty much what happened at Fatima in 1917.
What makes you think none of this it true?
Coptic icon of the Dormition of Our LadyAlthough the Assumption (Latin: ***ūmptiō, “taken up”) was only relatively recently defined as infallible dogma by the Catholic Church, and in spite of a statement by Saint Epiphanius of Salamis in AD 377 that no one knew whether Mary had died or not,apocryphal accounts of the assumption of Mary into heaven have circulated since at least the 4th century. The Catholic Church itself interprets chapter 12 of the Book of Revelation as referring to it.