User blog comment:Touchinos/"Ouroboros" Discussion/@comment-25027688-20190308213100/@comment-2605:A000:122A:408A:4950:9AD9:509E:BD89-20190311025417

The use of grace, its powers and its effects, have been both nebulous and inconsistent. It is possible there is no single correct answer to your question. However, Jack was not graceless. Lucifer did not take all of his grace. Jack's is regenerating, although the speed of its regeneration hasn't been specifically given. The idea and use of grace seems to have evolved from when Anna lost hers and Cas lost his. Perhaps grace isn't entity specific anymore--it just powers up whatever being has it (didn't Asmodeus become addicted to it?) Orion's metaphor of a blood transfusion seems the most apt answer to me.