Could also be that you were converted, and that’s usually the mark of a Marshal, especially if the Assassin/NK have been doing their jobs respectively. By D7 if both killers have killed someone every night you’re looking at 12 deaths, which would leave 4 players. If you’ve gotten that far with that many deaths as the 1st convert of Unseen then BD have fucked up not putting up the stalling Sheriff.
If you’re in a slow game where half those deaths have happened, we’re talking 6 deaths and 10 players, of which their will likely be 3 Unseen, and you will be unable to investigate the king so out of the 9 living players you’ve had 6 nights to hit 1 Unseen. That seems incredibly unlikely to me, and sounds like either your lying about who you’re investigating, aka your Marshal, or you have the worst luck in the world.
Heck we’re not even taking into account Scouting which adds an additional player that you can potentially catch as Unseen.
And as far as average deaths per game by D7, we’re also not taking into account Alch Bombs, Knight CSing especially in new patch, Prince jailing, King OE’s, Hunter Bears/Wolfs, and the Assassin killing anyone with poison, or Double Kill from Assassin.
I would say that 1 kill per night is actually very generous, and quite slow.