If you make a contextual update, an update to the timeline or substance of the story then you should update the Update Timestamp

Updates such as fixing typos, updating metadata, changing thumbnail, and making changes to stylistic components of the story should not warrant an update to the Update Timestamp in an effort to minimize reader confusion.

If you update your Topline Story, you will notice a toggle above the Update Button in The Publish\Update Drop Down Menu:

If the Update Timestamp Toggle is set to YES, the Update Timestamp of your Topline story will be updated, if it's set to NO, it will not be updated.
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