American Express reference number generation

Hi,

I was informed by American Express that the reference number received on the files received is generated using the transaction date, supplier and amount and will not always be unique. We are using the American Expression Loader and Validation program to upload the files, and it has a validation that looks to see whether the reference number and card number already exist. If the combination exists, then the transaction is not uploaded.

Has anyone else heard of this?

Thanks