There's no evidence the Apostles ever reached America or Lapland, for example, so there's still a long time between the New Covenant and the arrival of Christian missionaries to those places. Even if we're to accept that they miraculously preached to those peoples and left no trace, why would everyone thereafter be punished for their fathers' sins?
I'm not some BODer at all, I give (I believe the term is) faithful assent to the fact that not even the so-called "invincibly ignorant" can be saved. But it's still an issue I have trouble with understanding.
The term, "invincibly ignorant" used to mean something along the lines of "incapable of thinking", as in one who was born that way, or with a brain abnormality or deformity, or who was at some point in their life brain injured. For the last few centuries or so however, I.I. has taken on an entirely new meaning that includes "all those who want nothing to do with the Catholic Church".
The lie about I.I., in a nutshell, is that God rewards heaven to all those who do not seek Him, presumably because
"through no fault of their own" they never knew Him to even exist. After all, an essential part of I.I. is to mean that God is incapable of making Himself known to a certain of His creation, or incapable of prompting His own created beings (whom He created for heaven) to find out about Him.
"Through no fault of their own" are the key words which apply to all I.I. people, including lawyers, doctors and even teachers are among the ranks of the invincibly ignorant - but go ahead and tell them they are invincibly ignorant and, they will take that as a great insult!
We know that the Apostles fulfilled the command of Our Lord so that at one point, every one had the Gospel preached to them. We know this because that is what God told them to do - so that is exactly what they did. God did not miraculously transport the 12 Apostles all over the world *on foot* so that some might not get the message - and on that account be able to squirm out of it by claiming invincible ignorance! No, God said it, we believe it.
God also knew that some would reject His Gospel - "shake the dust..." remember?
So we also know that, like during the 2000 years since then, many/most rejected that same preaching for many of the same reasons it is rejected today. I'll stick with the old definition of "invincibly ignorant", at least that way, we can truthfully say that there certainly are invincibly ignorant people in the world.