For the original number to change you need to be using some sort of Automatic numbering.

The simplest is numbering tied to styles.
How to create numbered headings or outline numbering in Ribbon Versions of Word by Shauna Kelly

You could also use SEQuence Fields.

The first method can make cross-referencing even easier if the styles used are built-in heading styles.
Why use Microsoft Word’s built-in heading styles? by Shauna Kelly