Cancelled a 2008 Credit Memo

 The payables manager cancelled a credit memo from 2008 on 5/31/11.  So when balancing month end close, he is out of balance for the amount of the credit memo he cancelled.  He is asking how he is to balance when the cancelling a credit memo.  I could not find a reference to cancelling credit memos in the ap guide or if it will appear on the reports he runs at month end to balance (trial balance, posted payments, etc). 

The credit memo is from 2008 and I don't think would appear on any of the reports.  Am I correct or wrong?

Thanks for any input.