Your audit team is performing audit procedures related to a client's revenue for the month of April 2019. The visualization titled "Gap Detection - All Invoices" presents the client's master sequence of invoices with "null" indicating a missing invoice. The visualization titled "Gap Detection - Missing Invoices" presents the same data, but only the invoices that are missing ("null"). Beginning invoice number on April 1st, 2019 is #2816, and ending invoice number, April 26th, 2019 is #7845.

Why do a auditors care about prenumbering and gap detection?