iTunes Connect - difference between units sold and units paid out, plus Apples commision

I was wondering if anybody else noticed difference between units sold reported under the "Sales and Trends" section and what is actually paid out under "Payments and Financial Reports" section? I'm currently missing around 100 units, which equates to about $100-$200 loss. Does anybody know what is the best procedure to raise this issues with Apple, or better has anybody had similar issues and succeeded with Apple?

Secondly, I also noticed an increase in the difference between "Proceeds" and "Sales" on the "Sales and Trends" section over the last year. The difference in the amount has been between 40-50% and recently as high as 66%. I thought apple only takes 30% commission. How come there is such a discrepancy between "Sales" and "Proceeds"?

Thanks in advance.

The discrepancy is there because of several factors that you haven't accounted for, primarily:

• For some countries VAT is included in "Sales" and deducted before you get your "Proceeds"

• Some purchases might be refunded by Apple because of customer complaints - i.e. you will get 0% proceeds for these

• The currency exchange risk is yours. It might be that the exchange rate fluctates leaving you with less than the expected proceeds when converted to USD.