I've not read the other article.
Follow the steps in this one. They work!
How to create numbered headings or outline numbering in Ribbon Versions of Word by Shauna Kelly

It looks like the other article is similar, but not the same. You really do want to use Shauna's method. It has stood the test of time (as in more than 20 years).

At first, it seems difficult. I've gotten so I can just do it. I still glance at the article, though, to make sure that I do not miss a step.

Once you have the styles and numbering set, you can (and should) save it as a template for reuse.
Templates in Microsoft Word

Shauna Kelly's method is based on the groundbreaking and thorough work of John McGhie. You can find links to some of his work and much more on numbering here:
Numbering in Microsoft Word