Can't Add Specific PO Line Numbers

Hello, 

I am cleaning up old purchase orders with goods received, not invoiced. When I attempt to enter a bill, the system states I am missing line 2 of the PO. When I reopen the purchase order to add the line number, it adds line 11. Is there a way to pick a line number on a PO? 

The first screenshot is from the “PO History” tab. The second screenshot is from the “details” tab of the purchase order. 

Thank you, 

Michael