В Виманаваттху (одной из книг Кхуддака Никаи) содержится интересное пояснение о том, что Плод Вступления в Поток это действительно познание ниббаны. Если это так, то, скорее всего, в Каноне под вступлением в поток (или под глазом дхаммы) поздразумевается не только достижение плода, но и достижение пути (когда плод ещё не достигнут) - и все такие персоналии называются Сотапаннами.
*** In a fine well-built city situated between hills, an attendant of a noble king endowed with good fortune, I was highly accomplished in dancing and singing. As Sirima I was known in Rajagaha.
But then the Awakened One, the leader among seers, the guide, taught me of origination, of suffering and impermanence; of the unconditioned, of the cessation of suffering that is everlasting; and of this path, not crooked, straight, auspicious.
When I had learnt of the undying state (nibbana), the unconditioned, through the instruction of the Tathagata, the Unrivalled One, I was highly and well restrained in the precepts and established in the Dhamma taught by the most excellent of men, the Awakened One.
When I knew the undefiled place, the unconditioned, taught by the Tathagata, the Unrivalled One, I then and there experienced the calm concentration (of the noble path). That supreme certainty of release was mine.
When I gained the distinctive undying, assured, eminent in penetrative insight, not doubting, I was revered by many people and experienced much pleasure and enjoyment.
Thus I am a goddess, knowing the undying, a disciple of the Tathagata, the Unrivalled One; a knower of Dhamma established in the first fruit, a stream-enterer. Henceforth there is no bad bourn for me. ***