In dialogue of Koihime†Musō, it is implied that everyone belonging in the Three Kingdoms Era bears a True Name. although there are no given True Names of the males, like Kada, and the non-love interest females, like Kayū (Although, she's suspected to have the True Name of Miyabi).
Only those allowed by the bearer may refer to the bearer by their True Names, hence being "entrusted" their True Names. It is considered disrespectful, rude, and even outright sacrilegious to refer to others by their True Names without being entrusted, and could be justification for murdering the offender. Even the normally calm and composed Tei'iku (Teiritsu at the time) immediately started yelling at Kazuto to take back his words when he had mistakenly referred to her by her True Name, with Chōun immediately threatening Kazuto's life.
In dialogue of Sengoku†Koihime, similar to Koihime†Musō, it is implied that everyone in the Warring States Era bears a True Name. However, in contrast to Koihime†Musō, it is actually expected for others to refer to each other via their True Names, and it is rude to refer to each other by the names that they were (historically) named (called the Meaning Name (
While it is rude to refer to each other by their Meaning Name, it is not considered a heavy taboo to do so, and enemies tend to refer to each other by Meaning Name as a curse.
Due to this switch in context, according to Kuon, True Names could also be referred to as a common name.