The "In use" setting includes styles that have been, at some point, been applied to text in a document (or its template), even if they are not applied now. It's better to specify which specific styles should be shown or hidden in the Manage Styles dialog box.

For what it's worth, you can get rid of "In use" styles which aren't actually present in a document as follows: In the affected document, press Enter to add an extra paragraph mark (¶) to the document. Select all content, except for that extra paragraph mark, and copy it to a new, blank document.

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Stefan Blom
Microsoft Word MVP

Microsoft 365 apps for business
Windows 11 Professional