User blog comment:Jopjopjop/Volume 18 Spoilers/@comment-3965848-20150511212720/@comment-24502975-20150512132505

@Jop I'm aware it doesn't work like that; my point was that Ddraig's soul is necessary for BG's abilities to be used. If all of its abilities could be accessed without Ddraig's presence, then you can say that he's not used as the source of the power. But it isn't like that. Ddraig himself even stated that Issei's the first host who treated him like a living being instead of just a source for power.

Though I still say Boost/Transfer aren't his original abilities until/unless that's confirmed in the LN.