EDIT: I was wrong. Please see my reply further down in which I realise this.
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IIRC, people have never been able to vouch for flagged articles, only for flagged comments. You gain your ability to vouch for flagged comments once your reputation hits a certain cutoff; rarely, you might lose it if dang feels you are abusing your vouching ability.
I believe the only way to vouch for flagged articles, is an informal vouching process in which you email dang and try to convince him to turn the flag off manually. Sometimes, that works.
Sometimes you are able to vouch for articles, I think it depends on if it's flagged naturally or if it's flagged by an admin. I should add though that it being flagged by admins is less about political bias and more about the topic immediately resulting in a flame war.
I'm guessing it might also depend on the number of flags.
Since this site isn't open source (except for a very old version) we can only guess at how it works. But my guess is it might work like this:
1. Every time someone flags an article, it increments the "flagged" counter
2. Once the flagged counter reaches a certain threshold, it becomes flagged – but vouched is displayed to eligible users
3. If an eligible user vouches it, the "flagged" counter is decremented again – if it falls beneath the threshold, it is automatically unflagged
4. However, there is a second threshold, and once the "flagged" counter reaches that, then nobody can vouch it any more
And that's not mentioning the ability of admins to manually override, either by forcing an article to flagged (so vouching isn't possible), or by disabling flagging on it (so votes to flag it are ignored)
Looks like we're misunderstanding vouches, I guess when we recall seeing a flagged article with a vouch option, it was because it was both flagged and dead, if it's only flagged, there wouldn't be a vouch option since the main counter to flagging is upvoting.
In fact if you go to https://news.ycombinator.com/vouched?id=USERNAME it shows you what that user has vouched – but unless you are a moderator/admin (like dang), you get a "Can't display that" error if aren't USERNAME yourself. Whereas, for a non-existent user, it displays "No such user" instead
I definitely remember vouching comments too, but I can't find any similar link that records what they are.
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IIRC, people have never been able to vouch for flagged articles, only for flagged comments. You gain your ability to vouch for flagged comments once your reputation hits a certain cutoff; rarely, you might lose it if dang feels you are abusing your vouching ability.
I believe the only way to vouch for flagged articles, is an informal vouching process in which you email dang and try to convince him to turn the flag off manually. Sometimes, that works.