When I was in High school both Ozzy & Sabbath were pretty huge(Dio wa sin Sabbath at the time).I was just getting into Metal(1981-82) I never knew Ozzy sang for Sabbath(and alot of people my age didn't either)I thought Dio had been singing for Sabbath since the begining.When I found out Ozzy sang for Sabbath, I thought it was just a couple very early albums then it was all Dio after that.
Its funny how new generations of kids discover stuff.When "Holy Diver" by Dio was at its peak there were new kids getting into it not knowing he sang for Sabbath.Strange!