Should historical data be considered ambigious if not proven as fact? Simple question, if there is few data points that allow concrete hypothesis (ancient history has many), should the information always be accompanied by some sort of disclaimer? A example would be you often hear descriptions of early nomadic tribes based upon generalizations given by a conquering foe only, very little if any from the nomads themselves.
Any time you have a single source for information (generalizations given by a conquering foe), there is no other supporting evidence, and there are no counter-examples, then yes, it should be accompanied with disclaimers since the data is actually quite weak.

It would be like saying "John Smith reported the sky turned red just before the earthquake." This is far better than saying "The sky turned red just before the earthquake." The latter implies that there are multiple independent sources for the information where, indeed, there might only be one.