The signs of true Mahdi were given to us my Mohammad PBUH. These signs were given and they include items such as him not claiming the leadership role...among other signs.
I am not making these signs up ..I am just stating them as they were stated by the Prophet in ahadeeth. Everything that will happen was told to us by the Prophet during one of his lectures that lasted from fajr to maghrib. I am sure you can search the net and find the details from some reliable source.
Oh ok. But im not sure if i'll be able to find the answers to the questions im looking for.
Him not claiming to be mahdi will be a big chaos in the world. Each tribe, region , culture will have their own type of Mahdi. How can there ever be a consensus amongst the whole of Muslim Ummah regarding one Imam Mahdi who will not claim to be Imam Mahdi?... are we sure we havent missed him already?