What's frustrating about this topic is that even if Harry has a conversation with Thomas while he is in Demonreach, I doubt it they would talk about Ebenezer. They could, but it seems unlikely to me. So, it might only come up two books after Twelve Months; skipping Mirror Mirror, if it comes up then.
I reread the scene where Harry explains the blood curse to Thomas. Harry didn't mention the curse running from victim to parent and grandparent, so Thomas wouldn't have been clued-in from that conversation.