Structure of adenoids
I'm impressed to stumble upon someone who can do that with his tongue. And mainly because I can do that myself!

Looking at the images and feeling with my tongue, this rugged area you mention is definitely too close to the nose to be the adenoids.

So I googled a bit (well, more like a lot) and I found this cool webpage which details that area.
http://www.theodora.com/anatomy/the_pharynx.html
and I found this snippet of text:


  Above the pharyngeal tonsil, in the middle line, an irregular
  flask-shaped depression of the mucous membrane sometimes extends up as
  far as the basilar process of the occipital bone; it is known as the
  pharyngeal bursa.


I've found stones in my tonsils but never in my adenoids. What I've sometimes found was dried mucus adhered to it when waking up in the morning.
I believe those stones might be rests of food (which can't really get up there).
Maybe this green mucus you found was just dried mucus? Maybe a little infection on a particular day?
I hope you get the answer, since it's passed a quite long time since you asked :)