>>40613028Diancie, Hoopa, and Volcanion were all present in X/Y.
We literally knew about them shortly after release despiting hacking not being there yet when people found out you could search on the GTS and would get different errors for ones that existed and ones that didn't and then tried the known trademarks.
Are you getting confused with Magearna which debuted in Gen 6 media but was still a Gen 7 Pokémon just like Togepi wasn't Gen 1, Kecleon wasn't Gen 2, Weavile wasn't Gen 3, Zorua wasn't Gen 4 etc. etc.?