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.
1/12 Judas Priest
3/12 Deep Purple
5/12 Dan Patlansky
11/12 Dead Daisies