Need to skip sales order approval for closed lines

Summary:

We have approval rules defined for sales orders. However we notice that the sales order gets sent for approval even if there are closed lines alone.

Given below is a common use case:
1. User submits Sales Order
2. Approval is triggered as criteria is met
3. Sales Order is approved, processed, shipped and invoiced (line is closed)
4. Order is revised wherein:
a) Changes are made on attributes unrelated to approval criteria
Or
b) A new line e.g. Line 2 is added (but does not meet approval criteria)
5. Sales order is sent for approval once again upon submission.
6. Sales order is approved and Line 2 is processed further.