Here's part of the answer:
https://github.com/minimaxir/hacker-news-undocumented?tab=re...
https://github.com/minimaxir/hacker-news-undocumented?tab=re...
> A vouched submission/comment has its rank restored (and potentially improved as the vouch can counteract the effects of flags).
It seems a single vouch isn't enough to counteract the software on a 1-minute old dead submission.