Canon

A list of series can be found here.

Level 1 - Must be broadcast by Nickelodeon

 * Series broadcasted by Nickelodeon are canon. Anything exclusively broadcasted to another channel is not canon.
 * Example: The first four seasons of Doug are canon, the last three seasons are not as they were broadcast on Disney's One Saturday Morning block.

Level 2 - Adjacent media

 * Adjacent media made by the creators of the series (not by third-parties) are also considered canon.
 * Examples: Official websites and Word of God are canon.

Section 2 - Rectons

 * 1. New information overrides previous ones, as if the original never happened. This includes changes such as characters, locations, story, and names.
 * 2. Old information can still be considered canon if it doesn't explicitly contradict with newer content.
 * 3. Re-releases of older information do not count as retcons and don't fall under point 1.

Section 3 - Universes

 * An adjacent media series can be considered its own universe if it's got drastically different information from its source material.
 * Example: SpongeBob SquarePants (3D Collectathon) is considered a variant of SpongeBob SquarePants due to how different SpongeBob's Truth or Square interprets the events of the original show.