Gen 3:15, Gen 5:3-5
Noah's grandfather Methuselah lived at the same time as Adam. So Methuselah could receive the gospel directly from Adam. Noah lived at the same time as Noah's grandfather Methuselah. So Noah could receive the gospel from Methuselah. So Noah received the correct gospel from Methuselah.
Gen 5:25 And Methuselah lived an hundred eighty and seven years, and begat Lamech. 26 And Methuselah lived after he begat Lamech seven hundred eighty and two years, and begat sons and daughters: 27 And all the days of Methuselah were nine hundred sixty and nine years: and he died. 28 And Lamech lived an hundred eighty and two years, and begat a son: 29 And he called his name Noah, saying, This same shall comfort us concerning our work and toil of our hands, because of the ground which the Lord hath cursed. 30 And Lamech lived after he begat Noah five hundred ninety and five years, and begat sons and daughters: 31 And all the days of Lamech were seven hundred seventy and seven years: and he died. Gen 3:15 And I will put enmity between thee and the woman, and between thy seed and her seed; it shall bruise thy head, and thou shalt bruise his heel.
Gen 5:3 And Adam lived an hundred and thirty years, and begat a son in his own likeness, and after his image; and called his name Seth: 4 And the days of Adam after he had begotten Seth were eight hundred years: and he begat sons and daughters: 5 And all the days that Adam lived were nine hundred and thirty years: and he died.