Tier has always been an exception to this, you could have only ever killed the 1st 3, and still pull any tier, but no other item from any other boss.
The change this tier is that killing a boss fully unlocks not only that boss’s loot, but all previous boss’s loot. So if you kill only the skip bosses (kazzara, nelth, and sarkareth), you could still pull any item in the raid.
True last tier, this tier killing a boss also unlocks the loot from all previous bosses in vault.