IMHO, it doesn't quite look like jadeite. Have you tested its SG?
It might be a vintage or antique and well-handled piece of soapstone, which is/was used pretty often, too. With the style of carvings, it look more like a 'cottage' piece or something akin to "trench art" as the carvings are surface deep. Much of the Jadeite carvings are really intricate because of the arraignment of the molecules lending to its strength, or durability, allowing the piece to be-shaped.-
If it is indeed Jade, I might say it's really old but if it turns out to be soapstone or something else, it might in fact be a local "doodle" and no more than maybe turn of the last century, at most.
As far as value? I'm sorry, I really don't know. It seems I got caught up in the replies and gave you my opinion as to whether or not it was Jadeite - you seem to already know the material. As far as value all I can say is, I bid on several pre-Columbian Jadeite pieces in an auction that seemed really simple and not too valuable, and to my surprise sold for quite a bit more than I was willing to pay, so I'm not the best judge on Jade pieces.
Just my 2 cents!
EDIT: after looking closer at pic 2506, it does have some relief. I'll keep my orig. post up for posterity but will add that it may be jadeite but looks fairly old, before the use of modern day carving tools, more likely old AND perhaps made in a remote or very rural shop. The drilled holes on the periphery indicate it may have been attached to something, and maybe ceremonial? Iirc, the Tibetans do some skull stuff as a part of their religion and mysticism.
Examples below~