Ijma Of Usuliyyun
The whole point of his that I have understood is we need to make sure that the ijma and tawatur was actually present at the times of past. For example how would we know whether in the past they did 5 salah or not or if there was any ikhitilaaf on this matter that was silenced?
Why? Why can it not be lost to history? And how would we know that it has been reported without checking books which was my original question?