I am renovating a house in South Carolina and have a stip sum contract with my GC. I have line item costs broken down for each trade, but do not know the exact amount that each trade has been contracted by my GC. How do I request lien waivers from each subcontractor without knowing their contract value? Is it possible to leave the amount blank or "unspecified" and have each sub sign to show they have been paid in full? Will that be legally binding without an exact amount?