(Tellingly, at the Fatima Challenge conference De Carli referred to the bodies as carbonizzati—charred! Where did he acquire that detail?)
It's not in the text. Let's assume for a moment that it's not a creative invention of De Carli.
I think that it would be not very common to see charred bodies on the battlefield. Perhaps only in burned buildings, but not in the open. It's not common even today, and I guess it wasn't common in early 1900's. There were no incendiary weapons aside from Greek Fire, and that was last used in 12th century. World War II flamethrowers are the minimum required for this (first ever was adopted in 1911 and virtually not used in World War I.) A nuclear blast would also burn the bodies. It's not very clear how these unobvious effects could be predicted in 1917, and the available text doesn't contain those words at all.
“(Tellingly, at the Fatima Challenge conference De Carli referred to the bodies as carbonizzati—charred! Where did he acquire that detail?)”
Never said that.