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

I do use automatic numbering from styles. So that's not the problem.

I (somewhat arrogantly) contend that if you did Automatic numbering using styles following all of the steps in Shauna's article, you would not have a problem with one updating when you add or delete another. When you do this, you never touch those numbering buttons at the top once you have your numbering set. You use the styles.

You are welcome to post a sample document with the problem. I would suggest making a copy of your problem document and editing it to remove confidential or proprietary information.
How to attach a screenshot or file in this forum.


[Edit after reading Andrew's post.]
Yup, I was being undeservedly arrogant.

I didn't think of someone doing it that way.

If you use the built-in heading styles, you can cross reference to the heading and have it display the number. It would not help though, if you did as Andrew notes and try to insert a new heading at the beginning of an old one. That puts them both inside the bookmark.
Also, if you use the option to display bookmarks, it does not display these bookmarks, because they are hidden.
The bookmark is not generated until a Cross-Reference is created.