The disappearance of knowledge from human consciousness is a rare phenomenon, but there are recorded instances of knowledge which has evaporated. As a curious example, Pancirollus, writing in the 16th Century mentions that, among many other cases of lost technology, in the time of the Roman Empire a man who had invented flexible glass was presented to Emperor Tiberius. Tiberius condemned the poor man to death and ordered the destruction of all his products, considering that such an invention was detrimental to society.
A striking case of general human amnesia is that of Aristarchus of Samos (born 310 B.C.) who was the first man to declare that the Sun is the center of the solar system, and that the Earth and all the other planets revolve around the Sun; he also arranged the Earth and planets in the correct order of their distance from the Sun. This knowledge was fairly soon forgotten and only rediscovered by Copernicus – 1800 years later!
A couple of points on recovery values, via Voxeu.
‘Recovery value’ is a crude means used by some investors when evaluating sovereign default risk.