I know it happened in Japan before, and now it's in America with Zygarde as well, and that this might mean it will come to Europe after this too, but for some reason, in Europe only Zygarde is being given away at the same time as the entire distribution in America.
On the official U.K web page detailing the event, it says Zygarde is to be distributed for a week, then says the week is from May2nd - 26th, which is actually the three weeks all three are being given away in America.
Why are they doing it like this, and is it likely that after May 26th it will be Xerneas and Yveltal in Europe? Because the way it's being done seems like we're just getting Zygarde, but not the (currently) better two! And as shinies!
(This isn't a complaint.)