User blog comment:B214/High School DxD EX/@comment-26527700-20160115184200/@comment-27232228-20160116085202

I think that Azazel had already recognized Quarta far before Zenobia decides to use the surname again in Volume 19 (Griselda formally appeared in chapter 14, so a hand-wave by having Azazel talked with her about Zenobia beforehand is enough, at least for me). So a pre-Volume 19 setting is plausible.