Episode 0’s and Prologues
Episode 0s and prologues that air as part of an upcoming series are included in the main series entry, not separated into a single-episode entry.
Episode 0s and Prologues that were released in a different format from the TV broadcast (such as a web-only release or DVD-only release) are still accepted and fall under the relevant media formats of OVA, ONA, and such.
This means that the episode count will be one higher than on other databases, such as MyAnimeList, where prologues and episode 0s in the same series are separated into standalone entries.
Fate/stay night: Unlimited Blade Works 'Episode 0 - Prologue' which aired just prior to the rest of the season.
Boku wa Tomodachi ga Sukunai Episode 0 was released as an OVA alongside a volume of the light novel. As the format differs from the main TV series, it would have a separate entry.