1. The page numbering you describe is in a header or footer.
2. Every section has three headers and three footers even if they are not used. These three are different; text in one does not change text in another.
3. It sounds like you are using first-page and regular.
4. Something put in the first-page header/footer shows up only on the first page of that section.
5. If your first-page header/footer is linked to previous a change made in that section will show up in the previous section.
6. The link-to-previous setting is specific to each kind of header/footer. Each section can have this set differently in six different locations.

Header/Footer Settings Recap

Page Numbers in Word 2007-2016

If you really want a handle on what is going on, you could download and use the Word Toolkit for advanced management of headers and footers by Shauna Kelly and Bill Coan and others.