Scenario: A partner moves all of the channel customers AWS accounts out of the consolidated billing account and into their own payer account . The old consolidated billing block is then deleted and now they have a Full Account Family billing block, which results in a data gap.
For the transition month
Partner Generated Billing in this case should detect the two source payers and stitch the bills.
Also note, after the transition month you can set the billing block back to Full family if you decide to do so.