Hoopa movie has shiny Rayquaza and two Kyogres and Groudons, which means they arent unique.
Then we have HGSS event along a tournament that had Fantina owning Giratina, mening Creation Trio isnt unique.

So, I guess only Hoopa and the Lake Trio are the unique legendaries (dafuq), maybe Volcanion too, while the rest can have multiple roaming around, bending wheather and reality at will.

The hell