The 7 generations thing does not work in the end. We only have 6.

James, Spencer, John (born at 6 mnths in 1924), John (Costner), Kayce, Tate

Only 2 ways it could still work. One is if Michelle Randolph’s kid with Jack is also named John, and returns to the ranch at some point. Michelle leaves but sure, I suppose the kid could come back and be Costner’s dad.

Other way is if the premie ends up fathering a kid at 16, and his son fathers Costner at 15, putting John III’s birthdate around 1955. This is extremely unlikely, as John 2 was played by Dabney Coleman, who was 23 years older than Costner. But he was only in the series as a flasback, cast with a younger version of John 3. This implies that Costner’s father was born in 1924 - most Spencer’s son John, but a small chance that Michelle’s son with Jack will also be born in 1924.

I always wondered if George suspected Lorraine kept in touch with that Calvin kid from high school. I mean, Marty looks just like him, and not much like George. Marty would have been born about 12 years after Calvin disappeared for good.