The difference is that it’s very hard—often impossible—to easily demonstrate an absence, to show that something has never happened. What do you do? Go scouring the newspapers for articles that don’t exist? A claim that something does not happen, or that it happens very rarely, necessarily relies on a broad familiarity with the subject in question.
A claim that something did happen, on the other hand, is amenable to a much more specific type of support. In this particular case, the name of the team and the player concerned and the year it happened would, i think, be the minimum necessary to convince me of Ellis Dee’s claim.
Also, even in the absence of evidence, we can make evaluations based on what we know about our sources of information. I’ve been talking baseball on these boards for almost a decade, and i reckon that RickJay knows more about the sport than just about anyone here. In a conversation about the NFL, i would defer to Ellis Dee in a heartbeat, but when it comes to baseball, in the absence of independent evidence, i’ll take RickJay’s assessment most of the time.