Cardenio was known to have been performed at least on one occasion in 1613, by the King’s Men, the London troupe that Shakespeare wrote most of his plays for. The text was attributed to both William Shakespeare and John Fletcher, a playwright of equal fame during the time. Not much was known about the story of Cardinio, other than that it was thought to be a loose adaptation of an episode from Don Quixote, the first English translation of which had reached London in 1612.
In 1727, Lewis Theobald, a well known Shakespearean scholar and editor, claimed to have obtained three Restoration-era manuscripts of an unnamed play by Shakespeare, which he edited (with improvements) and released under the title Double Falshood. This had hardly settled the matter of the missing Shakespeare by any means, as Theobald refused to show anyone the three manuscripts that he claimed as his source and they were later thought destroyed in a fire in 1806.
What’s more fascinating than this is that we have as many of Shakespeare’s plays as we do. Given the fragility of paper and our generally moist climate, and the habit of religious fanatics for burning everything that disagrees with their narrow minded fairy tales, it’s amazing any literature has survived this long.
The old claims of bias against non western literature is silly in the face of all this. It’s not that academics or librarians have discarded non-European literature, it’s that so little of any literature has survived. It’s only by chance that some of Europe’s literary heritage managed to be preserved at all and we should appreciate what we have, not fret over why this or that piece was lost.