Lord of the Rings TV series gets multi-season order at Amazon

[William Cloud Hicklin]

As far as I can tell, nooooobody knows. My best guess, given that Christopher was alive at the time the deal was made, is that they have only Second and Third Age material

Although the events of that year remain to date very murky, it is clear that Christopher's position as head of the Estate ended almost exactly at the same time as the Amazon deal was struck.

Now, I can say with almost complete certainty that CRT would never, ever have agreed to this, not if Amazon, or anyone else, had offered him the entire US national debt in payment. Which leads me to conclude that either (a) Christopher retired due to advanced old age, and as soon as he was out of the way other family members jumped; or (b) Bezos came offering a quarter-gigabuck of cash, and the obstreperous old man was forced out because he stood between them and Smaug's horde.
And since the deal was made without Christopher it's almost certainly for the whole damn legendarium.