Like entry 5, entry 6 is a solid piece of of information. Perhaps the best tidbit of knowledge I gleaned was the part detailing the average size of Dark households and cabals.
It does raise my interest in the Great Rune War. While it happened decades ago and thus you probably aren't planning on dedicating a book (or even a significant chuck of time) to it, it seems like a great part of history to receive an Arcana entry. Was the GRW tied to a modern war, like WW1 or 2 (or a smaller war), or was it independent, fought largely without the general populace's knowledge? Was it confined to Britain, or did it encompass multiple countries?