'6) Usually, exact numbers of each role are not revealed. But as a general rule of thumb, the Mafia will probably equal about one-third of the total players, and there will only be one of each Special role. This can vary, however.'
I know I'm dead, but to clear things up, he's saying there's one Mafia left. It doesn't HAVE to be 7. The KP could more or less be counted as a special rather than Mafia in this case, just affiliated with the Mafia.
Remember, it doesn't EXACTLY have to be one-third of the TP.