https://news.ycombinator.com/item?id=10298512 Maybe that will answer your question. But just exercise common judgment, think of a possible reason as to why a particular thing was flagged [dead] to begin with, and then determine if it's unfair.
I usually have a higher bar for vouching. It has to be more than something that wouldn’t be flagged if that makes sense. Mainly because I don’t what my rep to get a hit. Something I think is ok might be a bad comment in the quantum HN mind.
Vouch early and vouch often.
You could always email the webmasters (see the contact link at the bottom of the page) and ask them if your vouching usage fits the intended use of the feature.