Hi there!
I have been using your book The Complete Guide to Yin Yoga for reference a lot. One thing that stood out to me from the beginning and still does is where did these main 15 or so poses (and variations) come from/ and do you ever practice yin postures that are not those?
I ask this because I practice yin yoga and the traditional poses but also sometimes I come up with an entirely new pose that is not in the book and wouldn't be a variation either but is extremely yin like.
I am not sure I completely understand your question, but I will give it a go. If you are asking where the 25 postures described in my book came from, the majority came from Paul Grilley's original book, Yin Yoga: Outline of a quiet practice. His 2002 edition has 20 yin postures and several yang counter postures. To these, I added a few others that I had come across from other teachers, and variations I came up with myself. I think if you added up all the variations, there is probably close to 100 different postures offered in my book (don't forget the wall yin postures and upper body yin poses). And, those are not the only possibilities. Many other teachers have developed yin postures and flows beyond what Paul or I teach.
Rather than think there are only a few “authentic, or “authorized, Yin Yoga postures, think of the way the yin philosophy can be adapted to postures. Any pose that is passive, relaxed (i.e. no muscular engagement needed), and that creates a stress in an appropriate targeted area and can be held for 2 minutes or more safely, is a Yin Yoga pose.