MyAnimeList sources and curates their data manually with the help of their staffs and users.
Their Frequently Asked Questions stated,
I can't find a particular anime/manga entry on MAL.
First of all, make sure the entry meets the Database Guidelines. Foreign productions (e.g. Avatar, Original English Language "manga") and Korean ...
AniList can filter entries in your personal anime list by any of the following criteria:
Status (All, Watching, Completed, Dropped, Planning)
Format (TV, TV Short, Movie, Special, OVA, ONA, Music)
Genres (Action, Adventure, Comedy, Drama, etc.)
Country (Japan, South Korea, China, etc.)
Year (I'm assuming this means the year the anime first started airing, ...