What happens is that the names of women often don't matter: they are only women. A title is apparently more important, and her actual name would not have been used outside her intimate family circle.

Take, for example, the Muslim/Arabic habit of referring to a woman as "Umm Hassan." This means "mother of Hassan," and she will be known by the name of her oldest son the rest of her life. Even big stars of movies and music are known as, say, Umm Kholtoum.

Take the early Imperial Roman Latin naming system, where all the daughters of one family had the same name, legally. All the sisters of Marcus Julius Caesarius would be Julia Caesaria. So would all his daughters. In practice, they had all sorts of nicknames for the girls around the house, and even legally they would be differentiated as "the elder", "the younger," or "third daughter of M. Julius Caesarius.

In early Japanese history, we cannot find out what the names of women were. The famous diarists of the Heian court are only known to us by patronymics or nicknames, often to do with places of residence.

So undoubtedly Terken Khatun had a name given to her by her parents, but outside the house she was known as so-and-so's daughter, then so-and-so's wife, then so-and-so's mother, if anyone bothered referring to her. As a cloistered woman, why would outsiders want to display too much knowledge of the ruler's hareem? So her title did well enough, so far as all those male historians were concerned.

I notice that they use the title Khatun, which makes me remember they are related to the Mongols, who had no trouble at all recording the names of women in their Secret History.

Source: Ingraham, People's Names