Today I noticed that "Shadow Plane: The Shade Asylum - Calburan's Prison" is a writ that's available from the writ agent in the Nomad but isn't available from the Shadow Plane writ agent. There may be others that are missing, but I don't have a character that can easily check at the moment.
Reading the writ text, it doesn't make sense to me why Cordor would care but the Shadow Plane writ agency wouldn't, particularly considering the other Shade Asylum writ is available from the Shadow Plane writ agency. At the moment It seems like something that unnecessarily and unreasonably blocks Underdark characters from doing the writ.