Does the information that comes from the primary sources archaeologists and historians use to find out what the Ancient Egyptians wore provide entirely accurate information about what was worn, and why or why not?
This is, of course, something for which we cannot know the answer. We cannot know what the Ancient Egyptians wore because we have little direct evidence. We do have some primary sources like statues and wall paintings, but we do not have evidence that can tell us how complete or how accurate the picture we get from those primary sources is. I would argue that the information that we get does not provide completely accurate information about what was worn.
There are at least two reasons for this. First, the kind of evidence we have is, in many ways, propaganda. When Egyptian ruler had art made that depicted them, they wanted that art to portray them in the best possible light. Therefore, they would have had themselves depicted wearing the sorts of clothes that fit with the image that they wanted to cultivate. We have to understand that this might have led them to have inaccurate portrayals made.
The second reason is more important. The people making these primary sources were not interested in leaving us with a complete record of what sorts of clothing were worn in all situations by all kinds of people. They were interested in creating images of what was important to them. Therefore, they would not have left us with much evidence about the clothing of unimportant people. They would not have left us with much information about the clothing worn in casual situations.
In a sense, looking at these primary sources is like looking at campaign literature put out by a politician. It shows those people (and not the less important kinds of people) wearing clothes that are meant to portray a certain image. It is not the same as looking through all sorts of candid photographs of people from all walks of life in a variety of situations.