The acetates were, I believe, auditioned by someone who knew what they were doing on behalf of BRI, and apparently nothing of interest was discovered.
OK, but do we know that the "audition" included the acetates in question? Bicyclerider, for one, states above that although "acetates in Durrie's possession were auditioned by Capitol and nothing new was found," the acetates discussed in this thread "were discovered later."
And of course, we have Andy's posts stating that in fact something very significant was found--and it's currently unreleased and unbooted.