> I'm sure if @Dang had spare time there would be a filter, during submission of a new link, to check whether the exact same link already exists.
There is. Duplicate submissions get redirected to the existing thread. Sometimes it doesn't kick in, for reasons obscure.
Some submissions get unnoticed and some others with the exact same link gain traction and start having comments and being upvoted.
I'm sure if @Dang had spare time there would be a filter, during submission of a new link, to check whether the exact same link already exists.