Not knowing is fine. Everyone has to find everything out for the first time.
The point I think is knowing, or at least being able to assess, what everyone else might know. Chances are, on a metal website, Rob "metal god" Halford having sung for THE metal band Black Sabbath is bound to be common knowledge.
29/5 Dylan Moran
3-6/6 Sweden Rock Festival
19-21/6 Graspop Metal Meeting