Achievement Fashion
So, if I’m correct, is this the one that requires you to have cultural armor? If so, are the sets on the same character? I’m assuming not if you have 2 tier three sets.
Just from looking at it, it looks like you need Tier 1, 2 and 3 on the same character. The easy way to test this, however, is to buy a piece of Tier 1 armor and see if it updates your total to 13. Thankfully you have 3 and 2 completed, as those are the most expensive.