In the book Complete Valley of the Kings, the author quotes letters between a priest/warlord running the area of Luxor toward the end of the new kingdom. Don’t have the references handy, but the implication is that this guy turned grave robbing from a fly-by-night operation to a mining indstry. he had his priests going around looking for any indication of a grave.
Since he was one of the high priests, the bodies were rewrapped, properly labelled to explain who they were, and buried in collective stashes. It wasn’t “concern for the thievery”, they were the ones doing the theiving and rewrapping, according to some theories. SO we find a dozen or more royal mummies in one of the VoK tombs; we find a huge collection in an unmarked cave on the far side of the mountain. They even slit open the wrappings, and dug inside the empty body cavity, to ensure they got all the gold they could. (Modern X-rays show they missed a few minor pieces of jewelry in the wrappings.)
King Tut’s grave was robbed at least twice by fly-by-night thieves. In each case, it appears the robbers were caught and the damage repaired before they got much. The implication is that this happened not long after his death, while the location was known but guards still wandered the area. A bit later his non-descript tomb entrance was covered by debris from a dig above his and forgotten. As a result, it was missed in the wholesale robbery that happened later.
We have no idea what was in the great tombs or pyramids. We have some hints - IIRC, there is furniture still intact (but no fancy painting or gilding) from one of the satellite pyramids of the great pyramid. There is the Solar Boat (and a second one, not yet unearthed) beside the Great Pyramid. yet the interiors are sigularly unremarkable. VoK is a great sight - 3500 years old, and all those tombs are full of paintings and heiroglyphics, many as fresh as the day they were painted. Even nearby nobles and commoners have decorated tombs. But the Giza pyramids don’t appear to have had any decorations inside. (Although there was an article afew weeks ago that one of the queen’s tombs, a mastaba nearby, had been opened and had carvings and artifacts but no gold.)
There is a gold-gilded wood sarcophagus in the Cairo Museum for Ankhaten - so some things survive by being lost by mistake.
Sadly, we have no idea what was in some of the other tombs, especially the pyramids.
Will they find more? I don’t recall the count, but it seems they have accounted for almost every pharoah from the era of the New Kingdom when these tombs were dug. However, on the other side of the ridge are tombs of Nobles, the Valley of the Queens, and tombs of rich commoners and VoK workers (including there’s a whole workers’ village where the foundations are still visible). They might not find tombs of the highest and mightiest, but they could find tombs from many of the lesser folk that somehow got forgotten and missed by the robbers.