Care to elaborate on that part? Sounds as if there were an interesting story behind that.
In short, there's simply too much guesswork being taken as fact and too many gaps in the evidence being bridged by assumption.
Case in point is the whole notion of the bubonic plague. The standard narrative is that there have been several outbreaks of this plague, with the most major ones occurring under the reigns of the Roman Emperors Marcus Aurelius and Ioustinianos, in the 1340s, and in China in the late nineteenth century. In many respects, the symptoms of these plagues as described by eyewitnesses match the fairly-well recorded Chinese outbreak. But, it must be emphasized, this does not apply for all aspects. In some cases, incubation periods are off; in some, skin color is different; and in others, the actual descriptions of the buboes, or pustules, or whatever (the naming conventions varied considerably over the centuries as you might guess) vary in themselves.
Usually, historical epidemiologists chalk this up to poor reportage and insist that the ancient or medieval chroniclers simply got it wrong in some ways. Apart from the fact that these are frequently very obvious things to get wrong or right, especially in the case of men who had the plagues in question (Prokopios of Kaisareia, for instance, contracted the plague of Ioustinianos and recorded its symptoms). And when you think about it, isn't it unlikely that the same exact plague would have continuously hit like that? Shouldn't there have been some sort of mutation at the very least - and possibly a whole other disease?
But if this disease was not the classic bubonic plague as described in Yunnan in the nineteenth century, then other assumptions that have been made about its mortality rates (relevant for historical demographers), spread, and even social impact may be anywhere from slightly off to catastrophically wrong. Even if it were just a mutation of some kind, all of those assumptions would have to be recalibered.
To emphasize the point, plague was found in an ice core dating to about the sixth century or so, and certain scientists were quick to point out similarities with modern stored plague. Many of the genetic differences went unremarked. The analysis is not, I believe, far along enough to be able to tell for certain about this plague, but it's looking more and more as though this plague was either the plague of Ioustinianos, but a different version than the 19th century plague, or it was neither of those and merely a contemporary specimen.