why this is unknown? (carlsen-caruana)

(move 67....)why its unknown?to see unknown click on endgame reference

Because there's 8 pieces on the board but so far only 7 piece endgame tablebases exist.

so why its working (see move 59)

It doesn't!? On move 59 it doesn't show any TB values either. (it could sometimes show something if a player has the option to capture because if he does, it becomes a 7 piece position)