Why does it matter if they inadvertently mailed someone an extra ballot or two? As long as they only count one per voter, who cares? I'd much rather them accidentally send a duplicate (knowing that they'll only accept one per voter) than for them to inadvertently NOT send someone a ballot, especially of the person's only access to voting is by mail.
ETA: I agree sending ballots to someone who has been dead that long doesn't look good, but would only be a problem if someone tried to use the ballot to place a vote on the dead person's behalf and the election office actually used it in their tally. I don't know if that has happened but that would obviously be wrong.