It's only considered a dupe if the story/topic/product release has had significant attention (front page presence and discussion) in the past 12 months. None of these posts got much attention.

See dang's comments on the issue for the official position:

https://hn.algolia.com/?query=dang%20dupe%20porous&sort=byPo...

Thanks for the informative post and link.

No worries! By the way, it's frowned upon if one person posts the same link repeatedly without getting any traction - eventually it just gets annoying, especially for people who watch the 'new' feed and keep seeing the same thing coming up. But the above posts seem to be submitted by different people, so it's all good.