I don't know anything about America or their building regs.,  so don't know how they go on.

Thinking back to the Sunday morning when I first heard of the fire, one of the first videos I watched was from someone in the adjacent tower.  It showed the side with the blazing cladding but also shows the corner and the next side around the block with what looked like a corner flat on fire.  The camera moves to show the flames heading up the cladding then goes back to the corner flat and shows the flat above on fire but the cladding on the second side is not on fire.  From that I would say that as well as in the cladding the fire was also spreading inside the block and moving up the ducts.