I like to share a little observation.
After about 2k chest in Ice Dome post the anniversary update, i have gotten all the new skins available in Tyria except for the new shield or hammer skins.
Prior to the update, I ran about 20k+ chest in Ice Dome and I have never gotten shield skins other than the summit shields (SSS and SWS), and for hammer I have only gotten Summit Hammer and Giant Slayer hammer. This is also true for axe skin as I have only gotten Summit Axe in Ice Dome.
This leads me to conclude that this game has a hard code drop table for Stone Summit enemies (maybe only in Southern Shiverpeak area) for shields, axe and hammer, and this applies to the new anniversary skins as well. So if you are hunting for the new anniversary shield or hammer skins, Ice dome is prob not the place you should farm as it only contains Stone Summit mobs.
i welcome other Ice Dome chest runners to confirm this theory.
Can you post screen shots of the bone idols you got?