Jehovah's Witnesses have reached all nations with the good news
The "Society" wrote back to me once, in the days when I used to send in my concerns. They said that
"Jesus words at Mathew 10.23 indicate that there will always be some territory to be worked and thus we cannot assume that all will be reached personally with the Kingdom message before the arrival of the great tribulation... Wtower 15.01.2000 page 13 stated that while untouched terrritories still exist it may be that in Jehovah's due time ...........If Jehovah chooses , he could see to it that the good news is spread in ways that we cannot yet imagine"
So there we have it, they say that the Almighty will call time whenever he is ready whether deserving people have heard it or not.
I can just imagine someone saying that they have (probably) reached members of all national groups - which is not to say they spoken to all of them