The canon of a franchise is a system of classification that separates official media products from unofficial media products and official releases that are "disowned" by the right holders or not intended to actually "happen" in the fictional universe. These systems serve to determine which characters, locations, events, etc. "actually" exist in a series' fictional universe. Many franchises have official canons established by creators of the series, companies owning franchise trademarks, and other sources of authority. Unlike many other franchises, the Super Mario franchise and its many spin-off series do not have an officially recognized canon. Therefore, arguments over canonicity (canon vs. non-canon) are purely speculative, and are of no importance to wiki articles. Instead of using canonicity to determine the inclusion of various sources in our articles or the manner in which the articles are organized, the Super Mario Wiki opts instead to focus on Nintendo's involvement in a given source. Any officially licensed appearance, including Super Mario Bros., Hotel Mario, and The Super Mario Bros. Super Show! are considered official because Nintendo either developed the product itself or authorized another company to use the Super Mario brand. In the context of the articles, all official sources can be considered canonical and should be treated as such by all users. The Wiki voted to organize sources by series, meaning that Super Mario 64, Super Mario Kart, and the Nintendo Comics System may each be in a different section of the article. However, this does not mean any source of information is more canonical than the other. In no way should the organization of wiki articles be considered an assertion of what is canon in the Super Mario franchise. Instead, the organization of an article is simply a way to convey information in the most effective and efficient manner possible.
Of course this does not mean there are not discrepancies between different installments of the greater Super Mario franchise. However, since there is no official canon, editors should not hold the events of one source to a higher canonicity than another, even if they disagree with each other. Discrepancies should be noted in articles, but not speculated on. Essentially, it is perfectly fine to include disagreements created by different media products and it is not the responsibility of the writers to fix continuity errors. The wiki's goal is to cover the entire Super Mario franchise, not to resolve discrepancies between different sources of information. Ultimately it is of no importance whether a particular source is "more canonical" than another source.
Information regarding the development of a source, such as pre-release and unused content (unused characters and other scrapped video game ideas, for example) should be appropriately documented in sections regarding the development of a video game, character, etc.
Lastly, it should be noted that, canonical or not, the Super Mario Wiki only covers official content, as well as unofficial but notable mainstream cameo appearances and knockoffs that have been acknowledged by Nintendo itself. Fan creations, such as fan-fiction, fan-made video games, or fan-theories, are not to be referenced within our articles.