User blog comment:B214/Volume 22 spoilers/@comment-201.215.165.7-20170213165134/@comment-3965848-20170215094452

Bottom line is the process of Lilith turning into a Devil was different compared to the Reincarnated Devils today, Lucifer was capable to fully transform someone into a Devil while Evil Pieces only go halfway, leaving their genetic bodies similar to that of a hybrid.

To go into specifics, I'm guessing Lucifer must've created a completely new body for Lilith from his own blood while Evil Pieces mixes the Devil properties into the host original bodies as well as heal any serious injuries and illness they may have.