Let's say a customer subscribes to an annual subscription in January but decides to cancel the subscription in May and asks for a refund. If you process the refund in May, would the months of January - April be retroactively updated to reflect this refund?
The answer is No. Processing a refund will not retroactively change the months of January-April. The totals for those months will remain the same. Only the months of May and after (until the billing cycle ends) will reflect the refund.