Well, Abraham had some early-gospel-of-grace material to draw from, like that God would bless the gentiles through his seed, that his seed was promised, that his seed was to be sacrificed. I'm more referring to those who never heard even that there was a salvation. Maybe there is no such group, since Adam and Eve were given the promise before any of their children were born. Many call it the "proto-evangelium", which is Latin for "first gospel".
Genesis 3:15 NKJV — And I will put enmity
Between you and the woman,
And between your seed and her Seed;
He shall bruise your head,
And you shall bruise His heel.”
But then, for those whose ancestors did not pass on the information to their descendants, are they still counted as having heard said gospel?