Hi,
As per the standard process TECO status restricts only the Logistics postings point of view , but it will not restrict in the financial accounting postings of actual/Revenue, But the status of FNBL is Final Billing , when there is no open items of invoices pending from customer. Since all the Invoices were cleared and Final Billing was set to the WBS Element. So you can set the TECO status even if you are having the open Sales order Items.But the automatic option of FNBL status setting option by default was not there in standard system, But you can check with user status functionality it might be helpful as per your requirement.
Regards,
vrkumar