Romans 10 puts it succinctly:
For whosoever shall call upon the name of the Lord shall be saved. 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?
Every place and people group needs a proclamation of the Good News:
Places that lack an in-place, in-language proclamation need a proclaimer.
It is best if the proclaimer is a person who shares their language and culture. It is good if at minimum it is a near-culture person who understands the situation. But if no same-culture or near-culture proclaimer is available, then a cross-cultural worker must be sent.
I believe we should do the hard work of finding the "nearest person" who can be sent, but if no one can be found or it's going to take years, then we ought
In terms of monitoring, we can over-complicate our databases. Really, the first and most important question is: does every place have a Gospel proclamation that can reasonably be expected to get into every language and to every person within a reasonable period of time (e.g. 10 to 20 years for every individual)?
Until we can know that about nearly every place, we don't really need to drill into further detail about any single place.