There must be a calculation or weight error. If you retrieve 3,943 mmol CuI then the amount of copper has to be the same or more but not less 3,915 mmol. Other way around 3,915 mmol Cu can only get the same number of CuI. The Iodine fits some how. 1,97 mmol I2 get 3,94 mmol I- approx. 3,943 mmol CuI.
The yield is oppsit by the way 100,72% or 100,08% Product/Educt.