Considering the fact that the descendants of Ujiyuki of the Yamana clan of Hoki Province used the letter '之,' as Toshiji (one of two kanji characters adopted by members of the same family), it seems that '氏之' was the original way.
加えて氏之以降の伯耆山名一族が「之」を通し字としていることも踏まえると「氏之」の表記の方が本来の姿に近いものと思われる。