The definition for legendary pokemon may be changing. The data shown by whoever was part of ProjectPokemon could have been a "blanket list" for allowing/disallowing the pokemon in the list for competitions. The "sub-legendary" term used was created by the guy who showed the list and wasn't actually in the data.
However, it is still very interesting which pokemon get a special background color in the SM and PokeBank Dex's. I'm unable to check right now because I'm too lazy to quit out of MMing in OR, but the PokeBank Dex only has holographic backgrounds for the Box legendaries, along with Mewtwo, Zygarde, and Necrozma(?). I cannot recall if there was a legendary category like there was one for shinies in the PokeBank dex. For the SM Dex: Magearna, Solgaleo, Lunala, and Necrozma all had a Yellow(?) background color. Zygarde too, or was that green? Type: Null and Silvally had a Green Dex color, and maybe even the UBs.
>>32518785I'm probably a Hoenn baby, but I wasn't too fond of the amount of legendaries introduced in Gen 4. Legendary Pokemon were seen as rare around those days.
>>32519161I've been told by various nerds that over in Japan, they've always used "Mythical" separately for event Legendary Pokemon.
