To monitor our return/refund/resend rates per month I use the Order Item Returns & Order Item Resends report from Query Data.
Further to this, to monitor the Refund rate I run the Refunds - Order Item Refunds (Actioned). However, as all refunds are included here, e.g. items that have been returned, there is a lot of overlapping.
Might I suggest the development of a report that incorporates all three reports in one? So that it notes all refunds/returns/resends but each is identified and easily sorted. e.g. if an item has been returned and refunded it is marked in one row and marked as refunded in an additional column?