The Canon Policy is WOI Wiki’s official stance on the canonicity of pieces of the Final Fantasy XV Universe. In fiction, canon is the material accepted as officially part of the story in the fictional universe of that story. It is often contrasted with, or used as the basis for, works of fan fiction and spin-offs.
In the past, the Final Fantasy XV community could declare anything developed by Square Enix as canon. However, as time passed, the Final Fantasy XV franchise branched out into more forms of media, such as anime, movies, novels, manga, short films, and other games. In doing so, aspects such as characterization, explanations, and plot points were inconsistent across all media—even amongst "official" works—and the clear classifications of what was canon became blurred. Increasingly, situations arose in what was stated in one official media would conflict with what appeared in another official media.
Arguments ensued about whether the inconsistency should be classified as a "plot hole," "continuity error," or "retcon." These inconsistencies are a problem particularly because of the way they can influence the viewers’ experience, especially when not consumed as a whole. Thus, World of Ignis sought a standardized system for determining canonicity in these discussions.
The solution was a canonicity classification system inspired by Star Wars’ Holocron canon policy and Narutopedia's canon policy. These policies assign different levels of canonicity to different media by considering different but licensed media treatments official and equally canonical within their own continuities but not across all continuities or the entire Final Fantasy XV Universe. This system is supported by Dan Inoue’s presentation on the Final Fantasy XV Universe, in which his team envisioned the Universe as "congruent" rather than a seamless narrative, as well as Akio Ofuji's statement about discrepancies in the Final Fantasy XV Universe.
WOI Wiki’s Final Fantasy XV Universe pages include five levels of canon, T-canon, S-canon, C-canon, V-canon, or N-canon, representing the level of canonicity of that element. T-, S-, and C-canon, together, form the overall ‘’Final Fantasy XV’’ continuity, with each ascending level typically overriding lower ones.
As an example of the levels of canon, in Brotherhood: Final Fantasy XV, a C-canon work, Prompto Argentum crashes the car after the group rides through Duscae. This work is superseded by Kingsglaive: Final Fantasy XV, an S-canon work, in which the car breaks down while Prompto is driving through Leide. That work is finally superseded by deleted content, a T-canon work, in which the car breaks down while either Noctis Lucis Caelum or Prompto is driving through Leide.
Language variations, particularly from the five primary languages (Japanese, English, French, German, and Russian), are each equally considered sources of canon; the Japanese language does not inherently trump the others. If information of the same level contradict each other and is not trumped by higher canonicity, in most cases, the information that appears most often in that level will be taken as canon. For example, the source of the name “Izunia” differs between languages in T-canon, but one explanation appears more often than the others and will be taken as canon. Nevertheless, the article will note such conflicts.
Level 1: Tabata Canon
Tabata Canon, or T-canon, is the highest level of canon that includes the “main game” Final Fantasy XV and any statements by Hajime Tabata, including unpublished production notes from him or his original, lead production staff (Shinji Hashimoto, Saori Itamuro, Takeshi Nozue, Tomohiro Hasegawa, Yusuke Naora, and Isamu Kamikokuryo) that may have never been seen by the public. Elements originating with Tabata in reference books, downloadable content, video games, and other sources are also T-canon, though anything created by the authors of those sources is S- or C-canon.
When the main game is updated, the newest editions are deemed to take canonical precedence over the older ones, as they correct mistakes, improve consistency, and express Tabata’s current vision of the Final Fantasy XV Universe most closely. However, downloadable content, special events, and collaborations are considered S- or C-canon, even if Tabata conceived the plot, unless it was incorporated into the Main Quest.
Deleted, or “cut”, content is also considered T-canon except if it conflicts with the main game or Tabata’s statements. Deleted content officially released via S- or C-canon still classifies as T-canon. Final Fantasy XV: Pocket Edition is also considered T-canon, except if it conflicts with the main game or Tabata’s statements, because it is a strict adaption of the main game and deleted content.
Level 2: Supplementary Canon
Supplementary Canon, or S-canon, refers to the second highest canon level comprising of the feature film Kingsglaive and the downloadable content Episode Gladiolus, Episode Prompto, Multiplayer Expansion: Comrades, Episode Ignis (except Episode Ignis: Verse 2), and the Royal Pack. S-canon elements also include statements from the directors of S-canon work and their lead staff as well as reference books, statements, and other sources which refer to those seven works.
As Kingsglaive, the Episodes, Comrades, and the Royal Pack have different directors and mediums, the people producing them will, at times, create new stories not found in the main game to explain things that are vague, expand on things to better fit the medium and audience, or alter T-canon content to achieve their own vision. However, the content is a higher tier than C-canon because it is heavily-promoted content that references Main Quest events. As such, characterization, explanations, and plot points given in S-canon content that do not contradict T-canon or admitted as N-canon can be presented as canon in articles.
Level 3: Complementary Canon
Complementary Canon, or C-canon, refers to the third highest canon level and last canon level of works considered as part of the continuity. It consists of all works under the name "Final Fantasy XV" that are not T-, S-, V-, or N-canon: books, comics, games, animations, trailers, plays, and more. Some examples include Brotherhood: Final Fantasy XV and the "Pryna’s and Umbra’s Snack Time" series. C-canon also includes any statements by lower-level staff and staff of C-canon work, such as Prasert “Sun” Prasertvithyakarn and Shinichi Kurita, including unpublished production notes that may have never been seen by the public
C-canon is similar to S-canon. They may create new stories not found in the main game to explain things that were vague, expand on things to better fit the medium and audience, or alter T- and S-canon content to achieve their own vision. However, as C-canon is a lower tier than both T- and S-canon, information from T- and S-canon supersede information in C-canon when there is a conflict between the two. For example, Brotherhood provides most of the information of the Chocobros’ younger years, and it is presented in the WOI Wiki as canon until a higher tier of canon replaces it.
Level 4: Versus Canon
Versus Canon, or V-canon, is material hailing from Final Fantasy Versus XIII, the Fabula Nova Crystallis concept, and the Final Fantasy XV 2013 E3 Trailer. Unless content has been specifically featured in T-, S-, and C-canon work, V-canon is not canon. However, V-canon is differentiated for N-canon because V-canon is Final Fantasy XV's unreleased and conceptual predecessor.
Level 5: Non-Canon
Non-Canon, or N-canon, is the lowest level of canonicity. It comprises of what-if stories, spin-offs, works not recognized by Square Enix as part of the Final Fantasy XV Universe, and anything else directly and irreconcilably contradicted by higher canon. Content that is explicitly labeled as "not canon" by Square Enix also falls in this classification. Examples of N-canon include Final Fantasy XV: A New Empire, the Official Comic Anthology, Episode Ignis: Verse 2 ("If"), Episode Ardyn, and The Dawn of the Future novel. 
Episode Ardyn, Episode Ignis Verse 2, & Dawn of the Future
Episode Ardyn and the Dawn of the Future novel is officially considered non-canon. In an interview, Takefumi Terada stated that any future DLC would be a non-canon "what if" type scenarios like Episode Ignis: Verse 2.  After Square Enix officially announced they would be producing new DLC, the Final Fantasy XV brand manager, Raio Mitsuno, said Dawn of the Future is the following:
To bring an alternate grand finale. Of course, we're not trying to overwrite the existing ending. The ending for Final Fantasy XV is the ending for Final Fantasy XV, but like we did with Episode Ignis, we want to give players a choice to see a possible different outcome. 
Finally, not only does Episode Ardyn and Dawn of the Future information contradict the main game, but the Final Fantasy XV scenario team did not finish Episode Lunafreya's scenario or start Episode Noctis' scenario. 
- 『FFXV』は新エピソードを制作！ 発売間近の『ロイヤルエディション』と『ウィンドウズエディション』についてキーマンに訊く. (2018, February 23). Retrieved July 11, 2020, from https://www.famitsu.com/matome/ff15/2018_02_23_interview.html
- Blinding Awesomeness. (2018, May 8). 【Final Fantasy XV】 PAX East 2018 Windows Edition: Making It Yours. YouTube. Retrieved from https://youtu.be/XSW6vE6zfdQ
- yuichiro_takeda. (2020, February 10). 言ってよくなったみたいなので公表しちゃいます……一昨年、『FFXV ･Episode II ルナフレーナ「自由という選択」 ・Episode III ノクティス「最後の剣」』のシナリオをご依頼いただいてたのですが、ルーナ編のプロットを書いたところで開発中止になってしまいました。無念…… [Tweet]. Retrieved from https://twitter.com/yuichiro_takeda/status/1226784654063071232