Start with meaning
A chapter holds concepts, examples, explanations and questions. A page layout is one expression of that material. If the layout becomes the only source of truth, every new format starts with extraction and repair.
Keep the relationships
Give each learning outcome a stable identity. Connect examples, misconceptions and assessments to it. Then a worksheet and an animation can refer to the same concept without copying the entire chapter.
Design for change
When an explanation changes, the system should tell an editor which resources depend on it. This does not eliminate review. It makes the right review easier to find.
A practical first step
Choose one chapter. List its outcomes, examples and questions before designing a new format. The relationships you record are the beginning of a reusable content model.