User blog comment:B214/Volume 21 info & spoilers/@comment-83.22.168.173-20160711150248/@comment-9595671-20160820224223

Actually, since the L for Vali's version comes from how he has the blood fo a Lucifer, I think the G doesn't stand for God, but for Great Red.

Issei's new body came from him, so I'm assuming the same is true for his blood. Atleast I think, I honestly don't know how blood applies in that case.