Well yeah, but.. surely them missing a shard (which is really something like a Naaru limb or something?) would be noticed... Not really an overabundance of naaru floatin about.
- - - Updated - - -
Oh shit. This has potential. If the Ashbringer was a cleansed Naaru shard like has been heavily alluded to..
.. and if Kil'jaeden was the one to originally craft Frostmourne... he would have access to that sort of stuff from earlier dealings with Ner'zhul...
Damn.