I'm not getting into the whole "Boris or Bela" thing again, 'cause that never ends well.  But I will agree that general audiences very often won't know who Lugosi is, or Karloff.  I've gone through decades of wives and girlfriends who couldn't get 'em straight.  It was always "is that Boris or Bela?"  She'd know it was one of 'em, but couldn't keep them straight.  And, with the exception of one girlfriend, it was the same with Cushing and Lee.  They'd know it was one or the other, but not which.

But it's also true, as more time goes by, that this becomes the case with other stars as well.  How many of the general population could identify Spencer Tracy?  How many have even heard of him?  I think somebody like Gable would score a little higher, but Gary Cooper?  I don't think so.  But this is the way it's always been.  I imagine that even a lot of us "in the know" sorts would stumble at identifying Conrad Nagel or Milton Sills or Bronco Billy Anderson.  It's just a by-product of the passage of time.  Very few, from any age or any field, have real long-term staying power.  Just because we know who Lionel Atwill was, doesn't mean that the other 99.9% of the population does.