The Table of Contents will generate a list of all your document’s headings with their page numbers. You can specify how many levels of headings to include, and there’s even a way to omit certain headings from the table of contents. But it can go tragically wrong if you forget to do one thing.
You could be forgiven for imagining that a digitally generated table of contents will stay updated, but it won’t. The table of contents and similar features in Word are generated based on a snapshot of what is in your document when they’re created.
So once your document is finished, make sure to go back to the table of contents, right-click anywhere within it, and select “Update.” From there you can choose to update the page numbers only, or update the entire table.
Most of Word’s “dynamic” features need to be updated this way, by right-clicking. If you have a number of these items in your file—such as custom fields that are managed through the File:Info:Advanced:Custom fields dialog and inserted into the document—your best bet is to select the entire document, right-click, and select “Update fields.”
If any of these are in the document header or footer, “Update fields” will not touch them. Instead, you have to pretend you’re printing the document. Hit “Print,” then quit before actually printing. This will trick Word into updating things in the header or footer. I don’t make the rules.