Generally we only use "already banned" when it's about the same case. So f.e. when a host gets reported for leaving in the same game twice, and he was already banned for it. Or when someone gets reported for leaving but he was already banned by the host.
When I handle a report about someone who's already banned I usually extend the ban. eg xxx is banned for leaving, 6 days left, and then afk's in a game: 5 days added to his ban for afk, bringing the total to 11 days.
stygian: that case is completely unrelated to this topic.