User blog comment:Jopjopjop/Volume 19 Spoilers/@comment-24173056-20141122062809/@comment-1359322-20141123005721

The Dragons wings originally could only appear on the BG Scale Mail after the Juggernaut Drive. You don't see Issei summoning out Dragon wings in his base form before this Volume. And the reason to that is probably because of his new body. Issei's new body is now a Dragon's body, he just gained access to the Dragon wings he previously didn't have access to which incidentally is the same as his BGSM wings.