Not in my experience. Multiple submissions (non Show HN) of mine have been second chanced. I can't be certain, but I don't think any of my Shows have been... I guess that says more about the content I create than the content I share.
Fair, didn't know that. But that proves some editing is in place, it could be a bit more active, perhaps.
Nope. If you email hn@ycombinator.com with the subject "second chance pool" and it is not your submission, there is a very high chance one of the lovely mods will take the submission and second-chance it.
Often enough, they even email the original authors and submissions about it if it is a really good submission!
Fair, didn't know that. But that proves some editing is in place, it could be a bit more active, perhaps.