Does the AI take my title and subtitle into account when it plans and writes the book?

From version 1.9.19, yes. When you give a working title or a working subtitle, they go into the instructions for the outline with one rule: every chapter must serve the promise the subtitle makes to the reader. Every chapter is then written with the same rule. A subtitle you gave is never replaced by one the AI proposes; a title you gave is kept as before. If you give neither, the AI proposes both from the outline, as it always did. Before 1.9.19 the AI never saw your title or subtitle while planning or writing. Chapters written before you changed the subtitle keep their text; the "Changed since the chapters were written" card on the book's page shows them, and "Does the book keep its promise?" on the Promise card tells you whether they still deliver it.