Hi Bill,
You are right there is no way to determine what happened there. Without disturbing the logic and design of GP we modified the cheque stub to include a description of the credit memo transaction and voucher number in order that both parties can follow the transaction.
Don't work yourself up though, I needed to go check with our AP dept to remind me why that change was done.
Ideally if a document type could print to show 'invoice' or 'credit memo' that would be more helpful.
Regards