This was the 'original' Sethyas story, that was being in much different format. It has little to do with the current in carnation.
The Order is:
Volume One= Vvardenfell
Volume Two= Mournhold
Volume Three= Solstheim
There wasn't enough room for the numbers initially apparently, as the series had a name change a year or two ago from "The tale of Sethyas Velas" to the original title I had in mind six or so years ago of "Memoirs of a Morag Tong Assassin."
But you do raise an excellent point. May need to bug Burnt Sierra aka BSD-IES again, or whatever name he's calling himself these days.