Tony Iommi has said that Michael Bolton tried out for Sabbath, but Bolton denies it.
Wouldn't surprise me the slightest as from mid 70s to mid 80s he was in hard rock genre. Only. And frankly, pretty good at it too. His band BlackJack was a bona fide hard rock band, lasted just a little while, with none other than Jimmy Haslip on bass (!??!?). Other members went on later to play the heavey metal circuit, and you know how incestuous the hard rock family can be, with revolving door members, and backing musicians, and bassists turn up in every other famous hard rock band there is. And since you have "contacts" from the past, you phone them up, and asks. He opened up (BlackJack) for Ozzy Osbourne a whole tour, so connections where made, for sure. In the autobiography book IRON MAN by Tony Iommi, Tony insists upon that Michael auditioned for them for real. Not just talking over the phone, and said no thanks, but ...you know... for real.
But it could be very well like this, like it was for Frank Zappa: He didn't audition every average Joe for his band. He had head of rehearsal, and musicians in his current band that where chosen to pick out the gems, that they thought would fit BEFORE Frank ever got a chance to hear or play with them. Sort of a filter. I can't think of that Black Sabbath was the same, since they were already an established band. It may be enough to do an audition for managers or some other musically inclined, to filter it out first.
Frank Zappa expressed opinion on this, since people could just "audition for him" to get on their cVs that they did!!! I mean, so hyped and level above anything else, was it, that it was considered a merit just to have auditioned for him, without ever getting any chance to get the gig. Zappa was monster hard on peoples sight reading skills. So he used this filter first, where it wasn't mentioned at all that they auditioned for Zappa, but for a bunch of anonymous musicians ..FIRST.