Most Christians do not understand the Bible very well, and many are not aware that they are not Christian. As I testify of the grace of Jesus and witness his love and Gospel I am amazed at how ignorant people are of the faith. I would expect this from a group who has not been reached, but not people in the modern western world. When I explain it to them it is as if they are hearing it for the first time. So is God then considering this interaction as actually "hearing the Truth" and therefore they are now held accountable for what they know.
I would almost venture to say that God gives each one of us an "A-ha" moment when it all clicks and makes sense and our hearts are ready to accept. It is at that point that our crucial time has come to decide on Truth. I think to some degree what may be happening is everyone is getting the "A-ha" moment to varying degrees based on culture contextualization. This is the moment we are held accountable too.
So the Truth of the Word of God is upheald. Grace through faith, faith alone in Jesus Christ.