User blog comment:Crimson and Darkness/Volume 24 discussion blog/@comment-73.49.228.11-20180107181327

Oh and somewhere on the forum.animesuki.com posts for vol 24, someone said "The other four extra demon clans apart from Lucifuge and Nebiros who served under Lucifer are: Agaliarept, Satanachia, Fleurety and Sargatanas. In myth, Agaliarept and Satanachia were the two demons directly under Lucifer, Fleurety serves Beelzebub and Sargatanas serves Astaroth. So maybe the Fleurety clan also served Beelzebub and the Sargatanas clan also served Astaroth."

And i'm pretty sure these guys are extra demons; dagon, samhain, & alastor(and maybe Diabolus and Apollyon(but then again they are other names for lucifer, so who knows)).

And maybe instead of satan(which is already being used as a title(maou/devil king) to describe the those in charge of the devils, maybe issei's title can be sathanus(another word for satan) or Satanachia(from the names above))