do it in several steps, without the AutoNumber() function:
- Sort the table by submission_date in desc. order (to have the latest date on top)
- Create a recordno() field to number the records
=> You can still use AutoNumber() if you want, but the recordno() should do as well.
The AutoNumber() fonction will create it's associated numeric values according to the order in which the different values of the expression received as a parameter are met. Simply preorder the data using a preceding load in the desired manner (latest vs oldest submission), and you shall have the desired result.