Suppose there is a common or a noble woman who conceived a child by the king, people who do not know who is the real father of the child may consider the child to be a son of a commoner or a nobleman. They will all realize, however, that the baby is a child of the king when the king himself declares the truth. By the same token, when the Lotus Sūtra informs you of those who are able to leave the triple world of birth and death or escape the cycle of the six realms and ascend the four realms through the pre-Lotus sūtras, it is all because the seeds of the Lotus Sūtra have been implanted within their lives throughout previous existences. Of the people who had planted the seed during their previous lives, those who are unresponsive and not able to attain nirvana through the pre-Lotus sūtras are able to attain enlightenment through the Lotus Sūtra during this lifetime. It is like a crown prince who was given birth by the queen but was raised by a wet nurse. The nurse is equivalent to the sūtras prior to the Lotus Sūtra.

Shōjō Daijō Fumbetsu-shō, The Differences between Hinayāna and Mahāyāna Teachings, Writings of Nichiren Shōnin, Doctrine 2, Page 197