Salve mi Piscine!
Well, that's one of the problems philosophy has been trying to tackle for years.
In a strictly rational sense, if you consider knowledge as something that is absolutely true, no knowledge can exist because of our own limitations (which may in turn just be concepts that are limited by our limitations... arg
).
I mainly think of "knowledge" as something scientifical, something that has been tested adequately and although may not be 100% correct, works (like Newton's gravity laws, for example). Perhaps the only domain in which this vagueness is absent is mathematics. But surely on an ethical and religious level, knowledge beyond the actual facts is very hard to debate about (and sometimes dangerous).
With regards to history, what qualifies as "facts" and knowledge depends on one's sources. For the largest part of historical facts, sources are absent. For some, we only have one source and if we're lucky we have more sources. The more the merrier, I'd like to think. However, in this cyber-age there's an almost cancerous growth of websites, so much that for many facts there may be a myriad of sources contradicting one another.
But I'm digressing. In a lot of articles I've read, some authors appear to confuse facts with opinions, or present opnions as facts. A classic example is Caligula's rule. Sources indicate that after a severe illness, his rule went downhill. Most think that he was barking mad. But there is no factual evidence for this (even though I don't believe the counter-theory that Caligula wanted to establish a hellenistic monarchy). We go by what people like Suetonius and Tacitus write.
Literary sources are not unreliable, but I personally think that in dealing with raw facts in antiquity, archeology and economic reports may be a good supporting source on historical facts and events. Although again economic reports can be false or missing. The best way to go may just be to do some own research and try to apply (scientific) logic. Sources may indicate some things, but I think they should be treated carefully. In order to do serious research on this, the researcher should also be familiar with possible tricks and traps. But then again... these may also be perceived.
I think our greatest problem is that the past is dead!
Scorpio