I think your talking about sources. Primary or Secondary sources.
The person always has a major effect on how the historian is recording the information. If we're talking about for example. The Chinese emperor here then if he'd had left a secondary source that someone else got then it most definitely wasn't in his perspective but in the perspective of another person. But if there were a secret journal of his then we'd know what his opinion was on certain things. The place also plays a huge role because we can know where the person set foot on and how that place had some impact on them. How that place was like back then. The time also has a huge value because whether it be the 21st century or 16th century, It matters based on how the world was back then or presently. The evolution as well.
I didn't really get what you were trying to ask but I hope this was somewhat close to what you were asking about?
