Shia Mahdi arising times

I believe we all remember report where Ali :RA Anho: suppose to say that concealment of Mahdi would last Six days or six months or six years

Here we have another interesting date from “Irshad” of shaykh Mufid.

Hadith 11: From Thalaba ibn Maymun from Shuayb al-Hadade from Salih ibn Maysam: I heard Abu Jafar (alaihi salam) said: “Between rising of Qaim (alaihi salam) and murder of Nafsu Zakiyah not more than 15 days”.

This hadith is very clear evidence that shias of time when these 3 narrators lived didn’t knew that there gonna be 6 more imams before al-Qaim would be even born! They wouldn’t dare to fabricate such hadith if idea of 12 imams and concealment of 12-th of them would be famous and known among shias.