Scattered throughout history are epidemics of catarrhal or campaign jaundice (the latter was experienced during military campaigns). The pivotal moment was during World War II where troops became sick with jaundice due to a contaminated Yellow Fever vaccine and sporadic jaundice outbreaks in different countries. While the symptoms appeared similar (ie jaundice), one did not confer immunity to the other and further investigation was needed.
This discover of Hepatitis A and B lead to the discovery of Non-hepatitis A and Non-hepatitis B: other illnesses that caused jaundice and liver damage. This lead to the identification of Hepatitis C, D, and E. Although they have similar names, these are 5 separate virus and require different tests for identification.