I'm all over the place with them, I first came across them round about book 12 or so, read the next few, then left them for a bit, and I still haven't read any of the ones before Falling in Love and after Through a Glass Darkly, although I did read the very first one last year. But a character from the first book features strongly in Falling in Love, which was why I wanted to read it now, whilst the memory of the character was still fairly fresh in my mind.