Watch Dogs had five days and it hasn't been released in Japan. (actually I'm not sure if their PR was based on the tracking weeks or a full week, but VGC data will be five days.) Mario Kart had 4 days in Japan.
Also if there had been a PC version of MK8 that sold 50k would that somehow make MK8 sales worse since it brings the average down?
I didn't count PC users, since that's impossible.