A few thoughts:
1. Calibration is not what most people think. Calibration has nothing to do with the machine identifying where an imbalance is; it only serves to calibrate the amplitude of the imbalance. Simply put, it better allows the machine to estimate if that amplitude is solved by .25, .50, etc.
If it over estimates you'll get a 180 degree on respin, if it underestimates you'll get an ask for an increased amount in the same spot. But never, will you get a request anywhere other than those two spots.
2. Balancing is not about reaching 0oz, its about repeatability (in reaching 0oz). You can have the assembly mismounted, balance to 0oz and then when you remount and spin get a weight request again.
This is indicative of poor wheel assembly centering (cone, offset rim bore X axis, off axis bore to cone).
Do you have pin plates?
3. In my assortment of collets, and cones, I often have 3-4 that fit "well" in any particular rim, but usually only 1 of them produces repeatability when dismounted, rotated, remounted and spun again.
Its rarely anything to do with who or where the cone was made and more to do with the shape or where it grabs relative to the rim bore.