If there is a relative who "disappeared" after a certain point in time, determine if there were any estates they might have inherited from after they disappeard. Was there a parent who died after the "disappearance?" Would the disappearing person have inherited part of an estate after they went "poof?" If so, the settlement of that estate would have required that they be found or at least their absence be explained. A cousin died in the 1940s with no children, and court records go into details about the searches made for his brother who went "poof" in the 1920s.