Old invoices appearing on aging report

[Coopfab]

After closing 2001 there now appears credit invoices for 3 customers all dated in 2000. These credit invoices were written off before closing 2000. This scenario may be hard to believe but it's true. The credits only appear in the A/R aging report not in the custmer ledgers. Issuing a bogus invoice for the credits doesn't work since the credit doesn't show in the customer ledger. Also, the credits do not figure into the A/R figure on the trial balance which is good. What can be done?

Thanks for your help and interest.

Michael Cooper