Moderators will sometimes rescue a post which didn't receive a lot of upvotes and reset the submission time on the post. This is part of an experiment in giving good HN submissions multiple
chances at the front page: https://news.ycombinator.com/item?id=11662380
No, at least not when my story was "re-upped", as they term it. The only indication that a story was rescued is observing the timestamp on the homepage vs. the timestamp on its comments page.
