At times, publishers/vendors may send a credit. This happens in a routine way most often for EBSCO, and occasionally other serials agents such as Harrassowitz.
Reasons for a credit:
Credits are handled exactly as invoices are, except instead of a charge against the funds, money is credited to the fund.
Dustin Reinhart processes credits.
At fiscal year end, it is common for Dustin to hold the credits until next fiscal year. This is especially true if the credits will put larges amounts of money back into the budget as we are working to spend down for the fiscal year close.