Summary
The Period sales reports are your primary reports for seeing an overview of the order activity in your account
When generating a Period Sales report (Current or Custom versions) there will be two sections in the report about refunds.
The are two refund sections in the period sales reports
Refunds (Original Order During this Period)
This refund section represents orders placed and refunded during the period of the report.
Refunds (Refund During this Period)
This one represents all accumulated refunds to date. This is meant to give you a idea of the true results of the sales of your products, but is not a representation of the refunds specific to the reporting period.
Special note about refund types and how they are reported
When you perform a "complete refund (the reject)" the original order and the subsequent refund are excluded from the sales reports.
(An example would be when someone places and order then calls you immediately after placing the order and requests that the order be cancelled and refunded. Since it was never really a order in that it was not fulfillment, you'd use the refund and then reject.
When you perform either a partial refund or a complete refund but the order is not rejected, then the original sale will appear in the sales report (if it falls within the reporting period) and the refund will appear in the report.