Possibly canonical links. HN looks at the submissions and updates the links to t...

		Jtsummers on Dec 26, 2023 \| parent \| context \| favorite \| on: A list of Hacker News's undocumented features and ... Possibly canonical links. HN looks at the submissions and updates the links to the canonical link if present. I'm on mobile so not able to double check the Google books page at the moment, but if you view source check to see if there's a canonical link in there. This also bites some blogging sites that end up with a canonical link to their base http://blog.example.com on all their posts. https://en.wikipedia.org/wiki/Canonical_link_element

Just checked and you are exactly right (it's not in the raw source but the element is found in the DOM tree). This explains the delay also!