Warning! As of 4/8/2017, if you complete construction and turn in the quest before your profession is at 800, you will not receive [item=147451], meaning the necessary mats to make the craftable legendary will be impossible to obtain. Hopefully they fix this bug soon!
Edit: Amazingly, this is either intended or they're not bothering to fix the bug. Here's the response from my ticket: "Game Master Palurriana here! I received the issue you recently hit us up about regarding you having some troubles getting the Armorcrafter's Commendation. I went ahead and took a look into this for you to see what was going on. It appears that the Commendation comes from completing the "Boon of the Nether Disruptor" quest, but only if your profession is at 800. Since the quest was completed prior to you reaching 800 in Tailoring, the item was not provided. The good news is that both the Nether Disruptor as well as the quest are available to be accessed repeatedly, so the next time the Nether Disruptor is built, you'll be able to get the Armorcrafter's Commendation and create a Legendary item."
Very disappointing.