It seems like Sunder Charms drop rate will be guaranteed if things aren't changed.
myzz7found this on another forum. hope its the case:
"it seems the devs have implemented a "Desecrated" tag associated with all champion, unique, and superunique monsters in Hell difficulty; when a monster is "Desecrated," it will always drop a Sundering Charm. It is unclear whether or not a Terrorized monster will be clearly labeled as being Desecrated or not (I'm guessing its just a hidden thing so you cant just tele around looking for a Desecrated mob).
This essentially means that the devs have a slider that they can adjust freely, possibly even set this value differently for different zones, mob types, champ/unique/SU/boss types, etc... and this slider will effectively control the exact droprate of Sundering Charms since each Desecrated monster will always drop one. I suspect that this is so that they can easily adjust different zones so that Andy/Duriel or other bosses dont heavily outperform Champ/Unique farming in terms of Sundering Charm drop rates. I also suspect that they will be much more common than previously suggested by the math of having rarity=1 (gheed's rarity + TZ and ilvl constraints)
If someone can find values attached to the Desecrated tag and how often each mob type/boss/etc is flagged with it, then we will know their rarity. But as this is probably a hidden value (easily adjustable server-side by the devs), for now we have no idea."
FuenteNo. They are not. Real drop rates aren't in client data. Drop rates are determined by the server.
This is just reflecting QA ensuring that the items do drop by setting them to 100% in terrorized zones, expansion only, etc.