Updating automatic table of contents
To update the table of contents--for example, if you changed the heading title or page numbers have changed: 1.Click anywhere on the table of contents, then click Update Table… Choose to update either the entire table or just the page numbers.
Want to add a table of contents to your Word document, one that can be easily updated if you change your doc? All you have to do is format your Word document appropriately. Format your document using heading styles found on the Home tab, e.g., Heading 1, Heading 2, and so on.
So, if you create a TOC before you're done with the document, the TOC quickly becomes out of date.