When using NBTedit to edit my max health from 20 to 30, it doesn't show the extra hearts. It still display 10 hearts although it still blinks to indicate regeneration, my health went beyond 20 and when I looked at the NBT data, it actually showed I have 30 max health.

Isn't it supposed to show extra hearts up to 20?

In the picture, the health bar doesn't show the extra max health.