The Scrooge McDuck Wiki, which you are currently browsing, covers a high number of works not published or licensed by the Walt Disney Company, but still held to take place in the Prime Universe which we cover.
Typology of non-Disney works
The vagaries of contractual copyrights means that although Disney retains ownership of most characters created in stories they produced, independent publishers, individual authors or other companies sometimes end up owning the rights to a "portion" of the Disney Comics Universe, enabling them to create further stories which were established by the earlier tale to take place in the Prime Universe, and remain implicitly so despite not including other, better-known elements of the Disney Comics Universe.
The historically best-known example of this phenomenon is the continuing adventures of Oswald Rabbit. Created by Disney's team of animators in direct continuity with the earlier Alice Comedies cartoon series, and sharing with it the character of recurring antagonist Peg-Leg Pete (who would go on to make the jump to Mickey Mouse), the series and character were, however, not owned by Disney. As such, following a dispute with the producers, Disney lost all right to the character of Oswald, though they would be bought back decades later in the 2000's, leading to Oswald and mainstream Disney lore's epic "reunion" in Epic Mickey (2010).
Thus, during the years he was owned by Universal Pictures and later Walter Lantz Productions, the character of Oswald was featured in countless cartoons, comics and tie-in products. Although not permitted to feature any other elements of the developing Disney universe (from Mickey Mouse to Scrooge McDuck), these stories were not meant as anything but the continuing adventures of the same Oswald who started out in Disney's Trolley Trouble, thus being implicitly set in the Prime Universe still.
Another case where large swathes of works not created under the aegis of, or even currently owned by, the Walt Disney Company, come to be seen as being set in the Prime Universe is through crossovers. When, as a unique "stunt", the Walt Disney Company or one of its representatives works out a deal with another copyright-holder to have Donald, Mickey or some other eminently Prime Universe character meet the cast of an unrelated fictional series, this is usually down as a special universe-breaking circumstance. However, it is sometimes the case that the crossover instead implies, or outright states, that the characters from the Disney and non-Disney series inhabit the same universe, with only geographical distance usually preventing them from meeting.
For example, the story Melting Pot, by Vicar, was created in tandem with Albert-René Productions and featured the meeting of Donald Duck and Asterix, with Donald crashing Gyro Gearloose's Time Machine in 1st century B.C. Gaul and naturally coming across Asterix and his friends. Especially combined with other allusions back and forth between Asterix and Disney comics in other stories, this is enough for this Wiki to deem that the Asterix franchise as a whole is part of the history of the Earth inhabited by Donald Duck in the modern day. We consequently cover Asterix media.
On the Wiki
With there not being any truly official Disney Comics canon, it is the $crooge McDuck Wiki's aim to present a wide selection of sources and data, and allow readers to pick and choose as they wish for the purposes of building their own headcanon universe.
Out of respect for the large numbers of headcanon-builders who would reject the conclusions of the Wiki when it comes to spin-offs and crossovers, information on this Wiki which is sourced to a non-Disney source will be marked out by the following tag: [NON-DISNEY], alongside the ordinary footnotes — allowing the reader to tell which information comes from a non-Disney source with a quick scan.
Similarly, pages that are either about non-Disney stories, or are in-universe content pages entirely derived from such stories, will be marked by the image-tag seen on the right, which will link back to the page you are currently perusing.