Difference Between Permalinks and Page Keys
Permalink
The Permalink functionality enables multiple pages with the same page title within the same space. We implemented another title, stored in the metadata of the pages, called Scroll Page Title. Basically, the Permalink is the "real" Confluence page title, and the one displayed in the UI when Scroll Versions is active is the Scroll Page Title. Scroll Page Titles and Permalinks are completely separate from each other. Unless you decide to change the Permalink, it will stay the same, no matter if you change the Scroll Page Title.
The Permalink has the pattern <baseURL>/display/SPACEKEY/PAGETITLE
Page Key
The Page Key functionality is another extra feature that comes with Scroll Versions, and does not have any conflicts with the Permalink. You can change both Permalink and Page Key independently of each other. For using context-sensitive help, we recommend using the Page Key functionality.
The Page Key has the pattern <baseURL>/display/_PK/SPACEKEY/PAGEKEY