Significance of title of book

On the surface, the novel's title represents Corinne and Annaleise who both go missing. However, it also represents the various version of herself that Nic has represented to others and then have disappeared as she assumes new identities. A version of herself first disappears when she leaves Cooley Ridge. Then she loses her accent and dresses differently. That version of herself disappears when she returns to Cooley Ridge and decides to stay there.