Up until yesterday I would have asserted that no one knows what constitutes a “chance” to hear the gospel. I was also less certain what the various statements to the effect that a people would be judged by the book that were written meant.
But then I was reading in Mosiah 3. An angel appeared to King Benjamin and gave him words to teach the people about redemption through Christ. It then states:
Mosiah 3:22 And even at this time, when thou shalt have taught thy people the things which the Lord thy God hath commanded thee, even then are they found no more blameless in the sight of God, only according to the words which I have spoken unto thee.
There we have a clear statement. His teachings constituted a “chance” to accept the gospel. That is what the phrase “they are no more blameless” refers to. When he delivered these words to the people, “even then are they found no more blameless in the sight of God, only according to the words which I have spoken unto thee”. Put differently, starting from that point they are no more blameless, unless they actually accept his words, and partake of the redemption of Christ through repentance and baptism.
We then get a fuller explanation of how this works, as well as an explanation of how a people are judged by the books which are written.
Mosiah 3:23 And now I have spoken the words which the Lord God hath commanded me.
24 And thus saith the Lord: They shall stand as a bright testimony against this people, at the judgment day; whereof they shall be judged, every man according to his works, whether they be good, or whether they be evil.
These words which were taught to them will also testify against them if they fail to accept them. “They shall stand as a bright testimony against this people at the judgement day”. Interestingly, it still states that they will be judged according to their works. They would be judged on what works they chose, based on the words that were given to them.
It sounds like the teachings about being judged out of the books which shall be written is at least in part a statement that they will be judged by the inspired teachings they had among them. Such teachings will “stand as a bright testimony” against those who reject them.