When people ask me if I have lived before, my first question is "Who am I?" (That can be a separate topic....)
Obviously, my body is unique at this time, so is there some essence that is passed from death to birth and on? My opinion is that Jung had it right by saying that we can (occassionally) tap into the deep subconscious where all is available.
When a person's ego is tickled by saying they were a princess in Atlantis the mind goes to work, possibly in dream states or doing breath work, or with hallucinogens. The experience may be real but not the experience of this actual person.
On another point, I am amazed at how many reincarnated Native American shamans I meet, or Pharoahs and Queens of Egypt but no boring ol' clerks in a 30's govt office...