Hi Michel,
As Neal has already mentioned, it is better to link back the confirmation number and counter to each record in your custom table.
You should also think about the way cancellation is done. In standard SAP, if you are cancel a confirmation, you don't delete the record or merely put deletion indicator on the respective record, but you post a cancellation record instead. So, in your custom table, it is better to put two additional fields: cancellation indicator and confirmation number and counter which cancels it.
Regards,
Julian