They are called "ooparts" and whenever they are found, they are conveniently "unfound" shortly thereafter.
What used to be a series of anecdotes in widely scattered references has now become something completely different because of the internet. Just as the UFO field fell apart when people had a chance to compare notes on the internet without getting the information secondhand, this field of archaeology has had life breathed into it as more and more people have been able to compile the data. It is apparent that this is not just an anecdotal story here and there but rather a colossal body of evidence assembled from everywhere in the world whenever somebody has dug a hole in the planet.
The same thing has happened with panspermia and Fred Hoyle's propositions. The internet has provided an indispensable hub where discoveries of amino acids, evidence of bacterial fossils and other anomalies in extraterrestial sources finally achieved critical mass and resulted in the orthodoxy tacitly conceding there is something to it. Of course this is after they have been destroying careers for decades in others who said the same thing earlier than they did.
I realized about 2002 that the evidence for ancient civilizations as complex as ours or better was abundant everywhere you looked and literally in plain sight. You couldn't miss it. People were so close to the trees they had long since learned to ignore the woods. The evidence was not compelling, it was decisive.
The confusing thing about our declining civilization is that there is so much use of ancient technology it appears most of the population has never really moved into the modern era at all.