If any of the three pieces of your Winter Garb set have 0 durability, you won't get the achievement. Every stored piece of Winter Garb I had in the bank, personal or Guild, had 0 durability when I took it out. I suspect Blizzard decayed stored Winter garb, there's no way they were damaged while I wore them in previous years. Don't waste Graccu's Mince Meat Fruitcake, Repair your Winter garb before you choke down the fruitcake!