@whburling

I apologize if the heated discussion with spillerbd is confusing or distracting you.
Back to your original question.

While the [Quick] Style Sets distributed with Word have a specific set of 25 styles, you can put as many as you wish in a custom [Quick] Style Set. They do need to be in the [Quick] Styles Gallery when you create a Style Set and will be in that Gallery when you use such a style set in a new document. This can get cluttered.

You can also use the Organizer to copy any styles from one document/template to another. You can do this with a macro if you want. See my page A Global StyleSheet in Microsoft Word? Doing this can allow you to create and import into other documents whatever styles you want with a single keyboard shortcut.

If you think you may have a need to dramatically change the look and feel of your documents explore Themes. Use Theme Fonts and Colors in your own styles to allow such changes. Avoid them if you want your styles hardened against such changes. If you need more on this feel free to write back.

After much testing... Microsoft® Word for Microsoft 365 MSO (Version 2301 Build 16.0.16026.20196) 64-bit
The StylesSet is composed of the Styles set to Show in the Style Gallery AND are saved as a Template file type in
C:\Users\%userName%\AppData\Roaming\Microsoft\Quic kStyles.

The last part of Styles being Saved in the document can be seen by examining the list shown through the Manage Styles, Import/Export option.
If starting from the Normal.dotm, there are essentially no styles in the Template. Any StyleSet created from a freshly started "Blank" document is very much that, Blank, including Styles! All the styles we see are the Applications Built In styles and they will not be saved into the documents XML until Modified or Used. A Unused and unmodify style can be set to be displayed in the Gallery, but will not be saved as part of the StyesSet because their is no Style in the document to copy!

It does appear that MS may have expected users to select an appropriate StylesSet from their list. Doing so will add the remaining list to get to the 26* "standard" Styles. (The TOC Heading style is missed in Charles Kenyon Style Sampler.)
Using the Normal.dotm StylesSet will only update the 3 styles as Default Paragraph Font style is only a reference.
Also, just adding a Style to the Gallery is insufficient. The Style must also be used or modified for Word to see it as different from the Application's built in style and save it to the Docuemnt for reference and copying.

This means that creating a Template from which StyleSets may be created from may require a lot more awareness than one may think.

A Robust Template will define all the Built In Styles and not rely on the Application to provide them. Also, if a Style is not Saved in the document, the Style will not revert back to the "default" builtin characteristics.
To add the Styles to the document, one needs to use or modify all the desired styles.
For a macro that does this see, https://www.msofficeforums.com/word-...tml#post173769 Thanks Andrew!
Modifying the macro to comment out the wdStyleTypeTable is likely appropriate for most users.

For most users, is using and therefore defining all builtin styles in the document necessary? No.
For what he OP wishes to accomplish, I believe it is.
Essentially it is the same as doing a VBA code without Explicit turned on. Each Style in the Template must be explicitly defined to ensure that if a style is used in a StylesSet it adots the new settings.

I would also say that a Robust Company Template would also explicitly define all the Built-In Styles in templates and even use the Restrict Editing feature to keep users from using Direct Formatting.

During my research, I found this Blog post. Overall, nothing new, but sometimes a different writing allows a new perspective. Changing your style in the new Word | Microsoft 365 Blog

Custom StylesSets can be saved in Subfolders in your QuickStyles folder.
C:\Users\%UserName%\AppData\Roaming\Microsoft\Quic kStyles
If you have MUltiple StylesSets to use with Multiple Templates, the number of StylesSets could get large, or maybe the StylesSets are not compatible with all templates/documents for your use.

At Startup of the appication, Word searches all files in the QuickStyles folder and list those files as Custom items in the StyesSet Gallery.
If a Folder and its contents is Set to be Hidden before the application starts, those items will not be listed. This can give you control of the Custom list each time Word is started.

Do not save any other files in the QuickStyles folder.

Thank you for drawing attention to that missing style. TOC Heading does not appear in the [Quick] Styles Gallery until it has been used, but is included in the standard [Quick] Style Sets, which still hold 25 styles.

I've updated the sampler and changed the screenshot in my previous post.

Here are the 25 styles is a standard set:

• Normal (1)
  
• Headings 1-9 (Only 1 & 2 shown in gallery until one above is used) (2-10)
  
• TOC Heading (but not TOC 1-9) - not shown until used (11)
  
• Title and Subtitle (12,13)
  
• Quote and Intense Quote (14,15)
  
• List Paragraph (16)
  
• Strong (character) (17)
  
• Emphasis, Intense Emphasis and Subtle Emphasis (character) (18-20)
  
• Intense Reference and Subtle Reference (character) (21,22)
  
• Book Title (character) (23)
  
• Caption (paragraph) (24)
  
• No Spacing (paragraph) (25)
  

The screenshot of the Sampler does not show the Title style but it is in the sampler.


Here is an expanded [Quick] Style Gallery showing all of the styles in such a standard set.

It looks like I counted "Default Paragraph Font" when using the Style Pane.
Odd priority considering it is not a Style to be modified, and only(?) changed through the Default Font action through the Font Window.

To me, the "No Spacing" is also odd. But, there it is!