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?
Mario Kart 8 came out on the 29th of May in Japan, 30th in NA and 31 is Aus. Just looked it up. Where did you get "Mario Kart had 4 days in Japan" from?
Gotta figure out how to set these up lol.