I'm not sure what you mean. Pre-modern people lacked the ability to determine precisely pathogens caused which symptoms, so the terms for diseases tended to be pretty generic.

Moreover, there is no definite article in Latin, the language of most chronicles, so you just see pestis, which a translator might give as "The Plague", but in fact can mean "a plague", and is in any case not synonymous with Y. Pestis, the microbe responsible for the Black Death..