You shouldn't process P9s until after the year end. You can save any P9s that you receive throughout the year in your On Hold folder until you come to process them.
Move P9s to On Hold
P9s come into your PAYE Online inbox, you can move these into the On Hold folder by following the below steps:
Click Payroll Menu, then click PAYE Online.
In the submenu, click PAYE Online.
To make the Move To field visible, in the Form Type drop-down list, select P9.
In the Move To drop-down list, select On Hold.
Press the Tab key.
Move P9s to the inbox and apply them to worker records
Once you've completed the year end process, move the P9s back to the inbox by following the below steps:
Click Payroll Menu, then click PAYE Online.
In the submenu, click PAYE Online.
To make the Move To field visible, in the Form Type drop-down list, select P9.
In the Move To drop-down list, select Inbox.
Press the Tab key.
Once P9s are back in your inbox, to apply these to the worker records click Update Workers.