I'm not asking you to speculate on anything.I don't believe it is complete yet. You're asking me to speculate on how God ccomplishes some of the things He does and I just don't know that.
1Co 1:21 For since, in the wisdom of God, the world through wisdom did not know God, it pleased God through the foolishness of the message preached to save those who believe.
It seems that now God has limited reaching people through the message preached.
Rom 10:13 For "WHOEVER CALLS ON THE NAME OF THE LORD SHALL BE SAVED. 14 How then shall they call on Him in whom they have not believed? And how shall they believe in Him of whom they have not heard? And how shall they hear without a preacher?
Those 3 questions above are rhetorical. The expected answer is "they can't."
So I am simply assuming that many generations of people in Australia, the Amazon Jungle, even American Indians and more, never had any preachers sent to them until the Europeans started sending them out.
Jim Elliot, was killed in 1956 while attempting to make missionary contact with the Auca people of eastern Ecuador. That was 2,000 years after Jesus died and rose again and they were just now being reached.