《孔子家语·本姓解》
所以微子和微仲虽然是宋公，但始终都用微子称号。到了稽即位，才开始称公。
故二微虽为宋公，而犹以微之号自终。至于稽乃称公焉。
Therefore, although Wei Zi and Wei Zhong were Song Gong, they always used the title of Wei Zi. It was not until Ji ascended to the throne that he began to be called Gong.