No atlas points for killing Boss area lvl 82

I got books 1-3. I did a lvl tier 16 waystone in a corrupted and irridated area. it said area lvl 82. I killed the boss and it did not drop book number 4.

What is going on, why do i not have specific ingame information where i get my points from?

I know i am not a the point yet where i am supposed to kil the pinnacle. There is one more book to get from maps but higher than pseudo tier 18 is not possible...

did you ever figure this out?

You need to kill Arbiter once to get the book for the last 2 points. This requires finding the citadels. After that you also unlock the Arbiter tree.