See though that is not so shocking. First of all you are really young so this would certainly cause a gap, and you possibly never got around to going back to it. I watch a Kids React video on Youtuube and see high school kids who have no idea who Nirvana were, that is trippy to me. I can wrap my head around you not knowing much Ozzy easier than high school kids not knowing Nirvana, cause they were so huge that one would think it would take a little more time for them to fade back into the popular consciousness even with now what a generation later. But it is age and the way we gather information to. So it honestly is to to odd for people under 30 to know more about some cool "underground" band that put out a cassette then they would be familiar with Ozzy.