These legendary items are hidden. As of the Potion of Speed update, the quests for hidden items all appear after the character reaches a certain level.
Previously, the quests to get them had secret triggers (conditions to appear) in campaign. In some cases, they were only available in multiplayer. In other cases, it wasn't clear whether / how to get certain hidden legendary items.
Please see Total War: Warhammer II items for more info on items in Total War: Warhammer II.
Pages in category "Hidden legendary items"
The following 6 pages are in this category, out of 6 total.