There are infallible revelations like the Blessed Virgin Mary experienced, but not necessarily Scripture (inspired public revelations). Very few Catholics know this.
They are dogma: “Absolutely certain and infallible special revelations” (Trent, Session 6, Canon 16).
They are infallible and absolutely certain. That is they contain no error and cannot be denied. Very few understand this import. They think that the only infallible revelations are in Scripture, but per Church Dogma (see above) they would be wrong.
Unlike General Revelation (Scripture and Tradition) these revelations apply to special circumstances and are individual to the revelator. There are special revelations that were shared between several visionaries (Fatima, La Salette, etc,), but they were not meant to reveal Scripture or Tradition (Catechism of the Catholic Church, paragraph 67).
Hence the name, they are private (individual to the revelators). They were messages indicated to increase devotion, personal virtue and sometimes communicate to the World (Akita, Fatima, Lourdes, La Sallete, etc). That does not make them obligatory for use (The Message of Fatima, Norms for Discernment of Revelations). This does not mean they are not infallible either.
Permission to Publish
All revelations in the United States do not need bishop approval (United States Catholic Conference of Bishops. Permission to Publish). Only textbooks require such authority. An ordinary may review such revelations, but is not under the obligation to do so.
Basic Discernment of Spirits
Here is the Basic Discernment of Spirits for Valid Revelations:
1) Orthodox (Dogmatically Correct): Lines up with Dogma (Nicene Creed, Apostle’s Creed, Ecumenical Councils, Canons of Trent, etc.).
2) Brings Peace (Supernatural): A papable supernatural peace defying explanation (natural causes), i.e. when there is war, you have peace.
3) Increases Virtue (Holiness). (See Catechism of the Catholic Church, 67). Conditions (Can Change Revelation). Virtue: Faith, Hope, Love, Ten Commandments, Beatitudes, etc.
A) Conversion (True).
B) Greater Holiness.
C) Greater Good (of Society, e.g. greater holiness, peace security, of everyone).
“[The soul or spirit is] intellectually transported; where is seen, without any evidence of the truth of the likeness of the body; [there are] no false opinions (Augustine, On Genesis, 26).
“[In] the intellect, however, the vision does not fail” (Augustine, On Genesis, 12).
“He means that intellectual vision which is possible to us, and having God in [our] thoughts; so in the case of angels, we must understand that by reason of their pure and sleepless nature they do nothing else, but always image to themselves God” (St. John Chrysostom, Homilies on the Gospel of John, Homily 15).
“These are revelations or purely spiritual visions and are communicated directly to the soul without the intervention of the senses, and thus, what God communicates through the spiritual ear is most profound and most certain” (St. John of the Cross, Spiritual Canticle, Stanza 13, n. 20).
“The effect of this speech was so powerful that for the time being she could not doubt its truth” (St. Teresa of Avila, Interior Castle, Sixth Dwelling Place, Ch. 8, No. 4)
“The miracles of Christ and the saints, prophecies, the Church’s growth and holiness, and her fruitfulness and stability “are the most certain signs of divine Revelation, adapted to the intelligence of all”; are “motives of credibility” (Catechism of the Catholic Church, 156).
Divine Communications (Types)
Locutions: Physical or Spiritual Voices.
Visions: Sights or Invisible Messages.
Divine Touches: Interior or physical touches
Other Miraculous Acts (Writing on the Wall, Apparitions, infused Knowledge, etc.)
Sense of the Faithful: From Pope to last of the Faithful.
A good read: Three Ages of the Interior Life, by Reginald Garrigou-LaGrange (Section 5 Covers these topics).