In most cases it looks like dang does give them a reason when they’re banned but I don’t think many of them read it.
Much more common is banned accounts that post a mixture of good comments and ones that break the site guidelines. Those, unfortunately, we can't unban, for the obvious reason that the bad comments do more harm than the good ones add value. That's why we introduced vouching: so the good comments can still make it through.
Sometimes we unban accounts and as soon as they're unbanned they revert to breaking the site guidelines. Then we ban them again and they start posting good comments again. The human heart has murky depths.
We can see whether someone else's comment has been killed whether we're logged in or out, so maybe I'm not following your question...