The dissemination of the Gospel in the 1st century took a long time. It didn't happen in a corner, that is for sure, but it didn't spread through the empire like a viral marketing campaign or movie trailer with 30 million views on youtube in a single day, either.
So, imagine for a moment, you're too old or sick or pregnant or had to stay home in your diasporan situation and couldn't make Jerusalem for Pentecost when Simon Peter preached. Before word ever gets back to you about Jesus and the resurrection and the Holy Spirit, you pass on, never knowing the New Covenant has been revealed and given.
Yes, it is appointed unto men to die and then judgment, but these I think could be said to have died in the faith, still waiting on the promises, no differently than any other OT saint. This is evidenced by, in
Acts 19, their immediate response and obedience to what Paul preached to them, that is, a demonstration and proof of faith, that saved them.
Now, once the Gospel was preached throughout all of Asia Minor and into Europe and Africa, the transitional period between OT and NT eventually ended, and there was no excuse. But before that period ended, how could it be any differently?