In "Gyokuyo", the diary of Kanezane KUJO, Sukemori is described as being the individual who was to succeed to the position of head of the family, and from the fact that he had already surpassed TAIRA no Koremori, who is thought to have been his older brother by a different mother, in official rank before December of the same year, it is considered that he was treated as Shigemori's heir from the beginning.
この時の九条兼実の日記『玉葉』には資盛を「嫡男」と記されており、また同年12月以前においては異母兄であるとされている平維盛よりも官位で上回っていた事から当初は重盛の嫡男として扱われていたと見られている。