One delight of historical research is that, of course, virtually no one will tell you something is unknown. (And if they did, you could not trust them. Perhaps your source is old, or the writer is not up-to-date.)
But what then? "A man will turn over half a library to make one book," said Samuel Johnson sagely, but what do you when you have turned over half the library, or even the whole one, and found nothing?
Do you end up searching in a dark room, at midnight, for a black cat that isn't there?
Historians have their own problems, but the rule for historical fiction writers is generally poetic license. Indeed, we have all read works where the writer used poetic license without hitting the library at all -- or worse, clearly hit the historical fiction section of the library for research. You can see errors propagating from work to work.
Sometimes by exaggerating a rare thing, or even a single instance, into a general custom. Remember that what people remark on is the remarkable, not the ordinary.1
Sometimes by misunderstanding something, down to not realizing semantic drift occurred.
Sometimes when someone simply made something up, and perhaps did not even realize it.
(The downside of reading historical fiction is that you do not even know that you do not know the truth. You absorb, through repetition, that medieval people thought the world flat, and then repeat it without remembering its source.)
And then there is high fantasy.
If you are closely adhering to a historical setting in your world-building, you face the same issues as a historical work, with a little more leeway because of your ability to apply magic or just apply spackle to shift it.
If you want to make your culture different, having perhaps more affinity for one culture than another, but still its own thing so that people won't tell you that you got your country wrong, you really are looking for a black cat that isn't there.
(Also, by the way, that won't work, people being perfectly ready and completely confident that they can lecture you about the laws in your own imaginary country and how feudalism works there.)
There are all sorts of titles that convey a culture -- marquise, Brother of the Sun and Moon, reverend elder -- and a position in that culture. What you want, perhaps, is a title that conveys your culture, and the character's position in it. Without conveying any real-world culture so strongly that everyone will simply assume that it's that culture with a bit of filigree.
But your culture doesn't map neatly. Useful for preventing assumptions, less useful for ripping off ideas.
The kingdom is not very formal. It's plausible that a princess, the heiress to the throne, has one dedicated servant of noble blood as opposed to several ladies in waiting, and other posts such as chamberlain and almoner. (Plus lesser servants, who do the work. In this story, they do not appear.)
What is the post held by this noblewoman?
Courts this small, ones where walking is feasible for getting through kingdoms, seldom have many titles. Indeed, they can lack titles for the king's wife, the king's sons, and the king's daughters and refer to them as the king's wife, the king's sons, and the king's daughters when not just calling them noble. (Henry VII's daughter was Lady Mary and only became Princess Mary when her Scottish marriage was arranged.)
Also, these kingdoms are also prone to be constantly at war, which my kingdoms aren't in this story. This is important because war affects travel, and there's quite a bit in this story.
So I inched onward a bit.
The queen does have dozens of ladies in waiting, which makes a convenient place for exposition, when some are new.
And true, a princess would have, as soon as she had her own household, half a dozen servants of high position, but then, she's merely nearly of marriageable age. So she doesn't have a household of her own. I can make do with -- hmm -- I'll call her a lady of chamber.
All this fuss for a trivial mention, because the woman, while an important character, is not important in the exact terms of her station.
Such is the researching side of world-building.
The Gentle Art of Reading Primary Sources
Having recommended reading primary source, I should warn that there's an art to reading primary source usefully. Lots of reading will give you practice at that, but this is to provide some pointers that will at least provide some aid at some point.
All this is important. One bad detail, like one bad ingredient in a stew, can ruin the whole thing.