When we look closely into the Fahua xuanyi 法華玄義, it is often mentioned that enlightenment can be attained secretly by people with the capacity of the two vehicles.
In the Tiwei boli jing 提謂波利経, which expounds the Five precepts and the Ten Good Acts 五戒十善 to lay believers in the secular world, it is mentioned that some have covertly reached the ultimate insight, anutpattikadharma-ksanti 無生法忍, that nothing arises or perishes. Zhiyi 智〓 acknowledged this fact and pronounced that enlightenment is possible even through Hinayana doctrines at the time of the preaching in the Deer Park 鹿苑時.
However, there is no conclusive verse or prose that can be seen as evidence in the Tiwei boli jing which clearly indicates that some have attained enlightenment within the early stages. Thus, due to the nature of its teaching as being unable to be discussed in words fully, it must be called the secret teaching.