Everything so far has been the import's own working copy. This turns it into real lessons, and shows you exactly what they will be first.
Read the Per lesson table: one row per lesson.
Layout (Tabs or Flat), how many components, answer boxes and Save buttons, and how many pictures still missing, with the totals above.
Select a row and press Show Preview to see that lesson as the patron sees it.
Nothing typed into it is saved - it is a preview.
Press Write N Lessons to the Library.
Back to the Model goes back a step instead. When it is written, Open the Library takes you to the book, and Images to add by hand lists what is left.
Finish any pictures listed as by-hand, in the Lesson Editor.
Publish the book when you are happy with it.
Until then the reader app cannot see it. Each lesson goes live as it is saved in the Lesson Editor.
Writing again after changing something MOVES lessons rather than copying them - what the old shape left behind is cleared out, and anything written by hand is never touched.
Discard Draft and PDF, once the book is written, throws away the import's working copy, including the pictures it took out, without asking. The library keeps everything already written; only the ability to write it again for free is lost.