I was looking for a question there somewhere and since I can't find any, I'll just comment on the 'thumb' thing.
I've mentioned a few times before -- 'from the mind to the body; from the body to the mind'
The exercises with thumbs and other parts of the body are Taoist methods to 'activate' certain centres of the mind through the 'intentional' exercising of specific parts of the body in co-ordination with breathing patterns -- i.e. 'from the body to the mind' Thus the numerous physical exercises found in Taoist chi gung, including Tai Chi Chuan, a body to the mind method, because of its application to MA, which is a physical thing.
Your thread on IMA/EMA has touched on this in a detailed way; I asked the question on the 'link' using the sanchin, naihanchi katas, remember. These katas are just a more elaborate ways of thumb twirling.
The Buddhist, on the other hand, chose the more difficult method of 'exercising' the mind in isolation first -- 'from the mind to the body'. They, initially, had no MA application in mind. It perhaps changed when it came into the hands of the Shaolin Temple martial monks, and when mixed in with Taoist methods brought to the Temple by outsiders seeking refuge there, we get all sorts of hybrids we see today.
"...the meridian to a particular internal organ" If done right, the practitioner should feel that particular internal organ warmed up, so you know chi is being intentionally directed to concentrate there. From my experience, the liver feels warmer than others. I don't know why yet. Any ideas?