Discovery in science means something different than discovery in common terms. Local people may have seen a snake for 500 years but if it turns out to be a new species, that is a discovery.
There also many Civil War-era battle and camp sites that local people know about but that archaeologists have not cataloged yet - they are not in history books and so the sites have not been officially analyzed. In Civil War CSI: Did Stonewall Jackson Die From Pneumonia?
I posted a picture of a bullet I found wandering around one of those overgrown sites in South Carolina that haven't been analyzed yet: