Storytellers are not obliged to tell all.
They choose to share or withhold details. They generally decide not to reveal everything when they allow for or mull over the possibility of a series. Details also emerge spontaneously as the storyteller progresses from book to book.
Or they find their inclusion influenced by avid readers requesting back-story data and prequel information. Such happens in the case of Tomie dePaola’s lovable, super-popular witch, Strega Nona. Grandma Witch is the artist – author’s own creation. So her inventor literally makes it up as he goes along.
Her popularity prompts her narrator to do what all biographers and celebrities do: gather her life history into the autobiographical, biographical “Strega Nona: Her Story.”