User blog comment:IamJakuhoRaikoben/Chapter 393: Silver Memories, Review./@comment-31.61.129.124-20140717084916/@comment-7418318-20140717103735

The knowledge about Deliora might have come from Ultear.

She was present at the incident, so she would know what happened at least in the broad details and at the time she was still part of Grimoire Heart, who were allies of Tartaros. Hades might have told them about Deliora as part of some negotiation or trade.