User blog comment:Jopjopjop/Volume 19 Spoilers/@comment-77.253.101.192-20141123093720/@comment-1359322-20141123111030

That is also because Ddraig left the ability intact for Issei

"[……Don’t worry…… I will make sure you can use the Boosted Gear even without me……. That’s why I’m glad I was able to see a good fight…….at the end……..]"

- Volume 12 Life 1.

So Ddraig can in fact rob Issei/other possessors of the ability to use the BG fully.