When viewing your Financial Stats, under the "General Stats" section of your dashboard page, there is a line item named "Store Credit Awarded". This number is a display of all the store credit given to customers through various methods.
This means that the following contribute to this number:
-Manual store credit adjustments
-Store credit payments for buy orders
-Store credit refunds
-Coupons that give store credit as the reward
Basically, anything that adds store credit to a customer's account is included in the "Store Credit Awarded" number.
Note that negative credit adjustments are not accounted for. So, if you manually subtract store credit from a customer's account, it will not affect the store credit awarded value. The same goes for store credit payments made by customers.