Think of history as many dots. These dots represent actual empirical data, history tries to order and connect these dots to a logic interrelation. The genuine nucleus of history are these narrations. History science tries to make the narrations as objective as possible. It is recognized by now that the subjectivity of language, location-bound comprehensive as well as multiperspectivity of sources and the selection of sources all plays into subjectivity. Therefore criteria were created to standardly write historiography. Nevertheless during my time at uni I got to learn many constructivists that were more of the "Hayden White Type". He called history science a "protoscience" and denied that historiography was any better than common stories, calling out contextualism and formatism (the preferred approaches to history for his contemporaries).

guesses, assumptions

Much of history. Thing is, common schoolbooks don't show the controversity in history but present almost anything as certain facts. I have seen classes that haven't talked about plausability once.

.potential misinformation from historical sources

Historians try to verify information by various sources. Often that is not possible though, so one has to put the author into perspective. Tacitus (important roman historian and senator) might talk alot of trash about germanics, we do know that by researching on tacitus, not on germanics, though.