Zelda sold through 1.8mil First Month in Japan/US for wiiu/switch. Game is doing well everywhere else, so sell through at minimum is another 700k (that is Europe, rest of NoA/World). That would be about 2.5mil+ sold. There are a ton of copies in the wild (pun nintended). So yes i believe we have somewhere between 3.6mil-4.2mil shipped+digital.
As of BotW selling faster, i think itll leg out well. Time to tell, it wont do under 6mil. Thats all i kno. Ill go with my prediction of 10mil. If it doesnt itll still be close imo
Where are you getting 1.8 million in Japan? Media create has it just under 500k through april 16.