cPanel PartnerNOC invoicing is run on the 15th day of every month. To ensure the upcoming invoice reflects an accurate number of accounts on each license, it is required that Partners review licenses 24 hours prior to invoicing. Should accounts be removed within 24 hours of invoicing it's possible removed accounts may be on the invoice and can't be removed.
Additional details about Partner Invoicing can be found in the following article: Partner Monthly Invoice