You’re quite right that they’re all very different from each other. In fact, I don’t think I’ve ever met two of their kind who are exactly alike. I talk about them as a group partially for convenience (it’s handy to distinguish them from my ‘regular’ clientele) but also because I believe they all have the same origin. Admittedly I can’t know this for sure, as my clients generally prefer to keep their personal affairs private. From speaking with the few who trust me enough to discuss such things, however, they appear to share a reason for not being fully human. At least, not any more.