Blizzard has confirmed that class set pieces can be acquired from the Great Vault raid row, even if you have not defeated the boss which drops that specific item. Great Vault Guide
Titus: Did we need to defeat a raid boss with tier on the loot table to be eligible for tier, or can it occur without defeating one? I did not get a tier boss down.Popping in to clear up a bit of confusion we’ve noticed from folks who are surprised the raid items in their Great Vault are coming up as Class Set pieces without having defeated the boss that drops that specific item. This is working as intended — because Class Set pieces are available from M+ and PVP, we wanted to ensure parity across different ways to play within the Great Vault and thus loosened the restrictions on boss-specific drops specifically for Class Sets.
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