Usually when I see a perfectly good, but dead, comment I check out the user's history. I usually see one of two situations here:
1. It's clear that they have a pattern of making nasty, off-topic, often vulgar comments. I'll still vouch for their good comments, but at least I can understand why they were dead to begin with.
2. If their history is of mostly normal comments except one bad joke at the start of their posting history that got them hell banned, then I'll vouch for them and let them know what's happened.