Deleted invoice does not show in the audit log

A customer received an emailed invoice. That invoice is no longer in QBO. I have checked the audit log, and that invoice does not appear to have been deleted or voided.

The customer never paid the invoice - he claims he mailed his check, and it never arrived.

The individual potentially had access to QBO - but it is my understanding that all deleted or voided transactions show up in the audit log.

How is it possible that an item can be deleted and not show in the audit log?

That invoice number doesn't show when I print a list of all invoices - the number before and after the missing invoice is in the report.