We know that many of the people on 316 are on the Hydra Island. Ceasar has been shown mostly in the Hydra Station reviewing files/reading/searching.
If you remember from past seasons, all the files that were referenced/reviewed by the others were kept there. When Juliet is seen with Jack's file, she is on the Hydra Island/in the Hydra Station.
That being said, do you think Ceasar has found the files of the survivors of flight 815 and is reviewing them?