 FAIR: It can appear to viewers that Einstein is a puppy in 1955 but  still alive 30 years later in  1985. However, the 1955 puppy is not Einstein but in fact a  different dog, Copernicus. You do not find out that he is Copernicus  until Back to the Future Part III when 1955 Doc Brown who, after  reading 1985 Docs letter, asks Marty who Einstein is.