Some styles have multiple tiers for weapons and/or armor pieces depending on what level they are.
Yokudan style has 1 tier for armor pieces but 3 tiers for weapons and shield. This is the same way Akaviri, Daedric, Dwemer, Primal and Barbaric style works.
However the Yokudan motif only creates tier 1 weapons and shields regardless of level. A level 1 iron sword and a cp150 rubedite both use the tier 1 icon gear_yokudan_1hsword_a and look the same, so it's not a ui only bug.
So one might think maybe they made the icons, but never implemented the ingame models for them, but if you go to the Seeker's Archive and look at the sword and shield mobs they have a kite shaped yokudan shield, which matches the tier 2 icon gear_yokudan_shield_b.