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If PickleRick's answer doesn't work for you, then you probably have some sort of setting activated in your document which tells InDesign to create a new section when you use a different master page. I don't want to complicate things unnecessarily, so I am not posting instructions about that here, but let us know if you try implementing this solution and it doesn't seem to work and we can help you continue to problem solve (if you do so, it would be really helpful for us to see a screenshot of your pages panel). – magerber Aug 8 '17 at 17:42

A best practice that we recommend to our clients is to create a base/folio master –with styled and positioned footers and current page number special characters– on which all other masters are based. This allows a footer that may contain date or issue information to be updated once and the changes are reflected in all of the master pages. If your masters only have current page number special characters then you can just add them to each master and the page numbers will be reflected when each master is applied to your document pages.

See Word's Numbering Explained by John McGhie, MVP - comprehensive and not pretty (Downloadable pdf file in letter size) - Reading this is vital to anyone attempting to use automatic numbering or bullets in a law office setting or other places where the documents are likely to be reused or heavily edited. See also How to Create a Template with a downloadable template with style-based numbering.
We'll work with the existing heading styles. When applying this technique to your own documents, you can modify the heading styles to reflect the properties you need—you're not stuck with the default settings. If, however, the built-in heading styles are already in use because you're working with an existing document, you'll have to create new styles. Avoid this route when possible. We'll be changing properties for the numbering scheme and not the actual heading styles.
Every time you save a document in Word, the information in the document properties is updated. Part of the information is a count of how many times the file has been saved. This is referred to as the revision number. You can insert the revision number in your documents and have it updated automatically, if you so desire. To insert the revision number in your document, follow these steps:
The standard method for displaying a page number in InDesign is to insert an Automatic Page Number Marker into a text frame (Text menu: Insert Special Character: Marker: Current Page Number). This is typically done on your master page(s) so that the page number will appear on every page using that master. If you wish to hide the page number on pages in your document, just use a different master that does not include the marker (or use the “None” master if you do not wish to display any master page items).
Changing the numbering display affects how pages are indicated in the InDesign document, as in the Pages panel and in the page box at the bottom of a document window. The numbering display also affects how you specify page ranges when printing and exporting the document. However, the numbering display does not change the appearance of page numbers on document pages.
To save the list style to a template so you can use it with other documents, select the list in the document. Access the Multilevel List dropdown and choose Define New List Style. Enter a descriptive new and select the New documents based on this template (at the bottom). Once you click OK, the multilevel list style will be available in all new documents.
CK Note: Word 2007 - 2013 interface has an different automatic numbering scheme which I have been told is much less subject to corruption. Microsoft Word 2010 Bible by Herb Tyson, MVP. However numbering is still very imperfect in these later versions. I still recommend following Shauna Kelly's step-by-step instructions (see above) if setting up numbering in a template or in a document likely to be heavily edited. If you start without doing this and end up with "spaghetti numbering," fixing it will be a very large chore!