No institution stands in command of the language more so than its newspapers. They, more so than even dictionaries, set for a mass public what words and concepts mean in common, everyday usage. Thus it is with "discover", in that Christopher Columbus is commonly considered to have "discovered" the Western Hemisphere, not because he was the first one literally to "discover" it by landing here like Leif Erikson, generally regarded as the first Eastern Hemisphere person to set foot on the Western Hemisphere landmass, but because Columbus' voyage resulted in a significant change in world history. While the Norse half-heartedly planted settlements, they did little to maintain them, so they died out. By contrast, Columbus' "discovery" galvanized Europe in a way that led to emigration, commerce, and colonization. Even those who insist on recharacterizing Columbus Day as "Indigenous Peoples Day" do so in recognition that Columbus' discovery greatly influenced subsequent world history in a way Erikson's discovery did not.
In other words, Columbus' contemporaries established his landing in the Western Hemisphere as a "discovery" via good publicity, just like New Englanders did with their claim to hosting the first Thanksgiving, despite earlier thanksgivings in St. Augustine and in Virginia which, because they were not promoted with good publicity, became forgotten footnotes in American history, like Leif Erikson's landing in what is now the Canadian Maritimes.
Virginia, particularly, lost its place as the "first" Thanksgiving because it gave up its place in line to New England by its refusal to honor Pres. Lincoln's 1863 call for a "Day of Thanksgiving and Praise". Even decades later, Virginia wanted little to do with this "Yankee holiday". New England earned the right to claim the Pilgrims hosted the first Thanksgiving, much like Columbus, with good publicity, so its version should be the one we acknowledge.