Nan is often short for Nanette, Anna, or Agnes; It doesn't have to be short for anything, either. But a lot of names are re-used between the different stories. Billie Dean Howard (a medium) / Timothy Howard (a monsignor) (originally O'Hara) / Moira O'Hara (a ghostly maid). Charles Montgomery (a corpse reanimating doctor) / Madison Montgomery (a corpse reanimating witch). Dr Day (a doctor) / Misty Day (a healer). We have two Lukes (both noble heros), two Kyles (both student victims), and two Fionas (both sociopaths). The list goes on.