Shauna's article gives instructions for bulletproof numbering. Unfortunately, it is not idiot-proof or child-proof. If you follow the instructions and if styles are used to invoke numbering in the document, it will work, every time. It is that second if that can get you. If people go back to the numbering buttons to apply numbering, it will break.

If you are attaching the styles to the built-in headings, make sure your users know about the built-in keyboard shortcuts to invoke them. If other outline-level headings, consider attaching keyboard shortcuts for those or making sure they show up in the Quick-Styles gallery.