A "living dex" is just one of each Pokmon, including each form of an evolutionary line, so you can import them into a new game and finish the Pokedex without any headaches.
I'm trying to get all Alola forms in Gen 7 as separate from the originals, but that's the only thing. I already have all Vivillion and Unown forms, but... Spinda? Isn't finding them all impossible?
Come check out my movie watchthrough topic:
https://gamefaqs.gamespot.com/boards/8-gamefaqs-contests/80167031