The anime's Pokédex takes parts of the games' Pokédexes to make up their own. I haven't checked all the anime entries, but I have checked about 3-4 from each region and they would (for example) take parts of the Diamond Pokédex and Pearl Pokédex to make a new Pokédex entry.
For example, Diamond Pokédex for Piplup: [Because it is very proud, it hates accepting food from people. Its thick down guards it from cold.]
Pearl Pokédex for Piplup: [It lives along shores in northern countries. A skilled swimmer, it dives for over 10 minutes to hunt.]
Anime Pokédex for Piplup: [Piplup, the Penguin Pokémon. Piplup is a proud Pokémon and an excellent swimmer, and it has a layer of down that keeps out the cold.]
I hope that helped. I researched most of this on the Bulbapedia.
Edit: This is not only for DP. Scorbunny's Pokédex entry has parts of Sword and Shield.