While I am just returning, and not 100% sure on this, had something similar with unlocking Ulmia due to her being else where for the Storms of Fate quest. So went and looked here http://ffxiclopedia.wikia.com/wiki/Quell_Your_Rage and noticed a few potential prerequisites for your cipher to work, as well as mention of possibility of you needing to complete up through "Exploring the Ruins". So might want to check to see if have everything done on there, and if so keep plugging along with the RoV stuff if that has triggered a flag for the AAGK to be unavailable.