This might just be a case of bad luck, but I have yet to see the Work Order world quest for rank 3 Potion of Concealment pop up (on the horde side).
Out of chance, I searched for potion work orders on wowhead, and it only found the wq for alliance side. The horde wq wasn’t even in their database. I don’t know if that actually means anything, or it’s just a bug in the system. I have no idea.
Has any horde player seen the wq for rank 3?