Ray:
In consulting with the Chief Accountant I found out there's no need to delete the records in question in a selective manner, as that operation needs to be done only once a year at the end of the business year. At that point the whole content of the table needs to be wiped out, which is what the DeleteAllPS page already does, so there's no longer any need to modify it.
Thanks for the offer, though, and thank you for your attention.