The Miracle of Lanciano seems inappropriate to me since it sends what I think is a wrong message. The real miracle is that what looks like ordinary bread and wine is changed spiritually. Saying that can be changed into ordinary flesh and blood seems contrary to that.In some cases, bishops cannot deny the obvious. The Eucharistic Miracle of Lanciano, or the Miraculous Image of Guadalupe, or Fatima, believers and skeptics alike where thousands witnessed the spinning of the sun that dried everything up during a rain storm, for example. But even those, common sense demands that investigations be carried out, it doesn't mean bishops have no discernment. Mary on a taco or stains on a cement wall are silly and not worth the time. Bishops usually step in when a large number of people are affected. Bishops can only determine if something is worthy of belief, they never say they must be believed.
Guadalupe was controversial for a long time. I'll cite Wikipedia which gives its sources if you're interested.
Our Lady of Guadalupe - Wikipedia
A more complete early description of the apparition occurs in a 16-page manuscript called the Nican mopohua, which was acquired by the New York Public Library in 1880, and has been reliably dated in 1556. This document, written in Nahuatl, but in Latin script, tells the story of the apparitions and the supernatural origin of the image. It was probably composed by a native Aztec man, called Antonio Valeriano, who had been educated by Franciscans. The text of this document was later incorporated into a printed pamphlet which was widely circulated in 1649.
In spite of these documents, there are no written accounts of the Guadalupe vision by Catholic clergymen of the 16th century, as there ought to have been if the event had the Christian importance it is claimed to have had. In particular, the canonical account of the vision also features archbishop Juan de Zumárraga as a major player in the story, but, although Zumárraga was a prolific writer, there is nothing in his extant writings that can confirm the indigenous story.
The written record that does exist suggests the Catholic clergy in 16th century Mexico were deeply divided as to the orthodoxy of the native beliefs springing up around the image of Our Lady of Guadalupe, with the Franciscan order (who then had custody of the chapel at Tepeyac) being strongly opposed to the outside groups, while the Dominicans supported it.
The main promoter of the story and those native believers was the Dominican Alonso de Montúfar, who succeeded the Franciscan Juan de Zumárraga as archbishop of Mexico. In a 1556 sermon Montúfar commended popular devotion to "Our Lady of Guadalupe," referring to a painting on cloth (the tilma) in the chapel of the Virgin Mary at Tepeyac, where certain miracles had also occurred. Days later, Fray Francisco de Bustamante, local head of the Franciscan order, delivered a sermon denouncing the native belief and believers. He expressed concern that the Catholic Archbishop was promoting a superstitious regard for an indigenous image:
The devotion at the chapel ... to which they have given the name Guadalupe was prejudicial to the Indians because they believed that the image itself worked miracles, contrary to what the missionary friars had been teaching them, and because many were disappointed when it did not. https://en.wikipedia.org/wiki/Our_Lady_of_Guadalupe#cite_note-FOOTNOTEPoole,_p._60-24
The banner of the Mexican conquistador Hernan Cortes from year 1521, which was kept within the Archbishop's villa during the time of the Guadalupe apparitions.
The next day Archbishop Montúfar opened an inquiry into the matter. At the inquiry, the Franciscans repeated their position that the image encouraged idolatry and superstition, and four witnesses testified to Bustamante's claim that the image was painted by an Indian, with one witness naming him "the Indian painter Marcos". This could refer to the Aztec painter Marcos Cipac de Aquino, who was active at that time. But "if he did, he apparently did so without making a preliminary sketches – in itself then seen as a near-miraculous procedure.... Cipac may well have had a hand in painting the Image, but only in painting the additions, such as the angel and moon at the Virgin's feet", claims Prof. Jody Brant Smith (referring to Philip Serna Callahan's examination of the tilma using infrared photography in 1979).
Ultimately Archbishop Montúfar (himself a Dominican) decided to end Franciscan custody of the shrine. From then on the shrine was kept and served by diocesan priests under the authority of the archbishop. Moreover, Archbishop Montúfar authorized the construction of a much larger church at Tepeyac, in which the tilma was later mounted and displayed.
The report of this 1556 inquiry is the most extensive documentation concerning the Virgin of Guadalupe from the 16th century, and significantly, it makes no mention of Juan Diego, the miraculous apparition, or any other element from the legend.
In the late 1570s, the Franciscan historian Bernardino de Sahagún denounced the cult at Tepeyac and the use of the name "Tonantzin" or to call her Our Lady in a personal digression in his General History of the Things of New Spain, in the version known as the Florentine Codex.
At this place [Tepeyac], [the Indians] had a temple dedicated to the mother of the gods, whom they called Tonantzin, which means Our Mother. There they performed many sacrifices in honor of this goddess ... And now that a church of Our Lady of Guadalupe is built there, they also called her Tonantzin, being motivated by those preachers who called Our Lady, the Mother of God, Tonantzin. While it is not known for certain where the beginning of Tonantzin may have originated, but this we know for certain, that, from its first usage, the word refers to the ancient Tonantzin. And it was viewed as something that should be remedied, for their having [native] name of the Mother of God, Holy Mary, instead of Tonantzin, but Dios inantzin. It appears to be a Satanic invention to cloak idolatry under the confusion of this name, Tonantzin.
Sahagún's criticism of the indigenous group seems to have stemmed primarily from his concern about a syncretistic application of the native name Tonantzin to the Catholic Virgin Mary. However, Sahagún often used the same name in his sermons as late as the 1560s.
In the 16th century and probably continuing into the early 17th century, the image was modified by then adding the mandorla-shaped sunburst around the Virgin, the stars on her cloak, the moon under her feet, and the angel with a folded cloth supporting her — as was determined by an infrared and ocular study of the tilma in 1979.[
I can't reach a judgment either way on Guadalupe. Fatima is interesting since most people saw something; but some people didn't see anything.
That tells me it was probably more a vision rather than physical events. http://johnhaffert.org/wp-content/uploads/2013/08/Meet-the-Witnesses-91511.pdf#page=90 -- has several eyewitness accounts. The Lady of Fátima & the Miracle of the Sun
Not everyone reported the same thing; some present claimed they saw the sun dance around the heavens; others said the sun zoomed toward Earth in a zigzag motion that caused them to fear that it might collide with our planet (or, more likely, burn it up). Some people reported seeing brilliant colors spin out of the sun in a psychedelic, pinwheel pattern, and thousands of others present didn't see anything unusual at all.
That's what I'd expect. I don't think Jesus appeared to anyone except his followers after the resurrection. Some things are not meant for the eyes of everyone. I've no doubt Mother Mary could have appeared in a solid physical body if she wanted and made things happen in the physical world; but I think it was more a vision of a spiritual reality for sincere believers. I'd expect accounts to differ slightly if it was a vision, since even prophets have to develop their gift of spiritual sight as you can see in Jeremiah 1. For me, the fact that there are slight differences validates the apparition rather than undermine it. People are different and their minds are different; so when the prophetic occurs, it is colored by the people's mind. Each person has a uniqueness that God values. When to get suspicious is when too many people say the exact same thing as they did in 1 Kings 22. The prophetic does not come with exact words like that. It comes as an idea that the mind then translates into human words or pictures.