Stored Materials & Lien Rights

We are sending a large amount of framing materials to one of our customers wall panel plant facilities. The wall panel facility and the actual project are both in Massachusetts. My customer is receiving the materials now for a project that is not going to start until May. The GC for this project has agreed to pay for stored materials. As the materials ship to the wall panel facility my customer will submit proof of delivery for whatever materials they have received with in that particular requisition time frame. Playing devils advocate, what happens if the GC doesn’t pay for the stored materials ? Can we record a lien for materials that are not physically on the job site ? We have a credit application, a sales contract, and all the invoices show the ship to address as the job site address. We have all the necessary paperwork to record a lien but in this particular example the materials are not physically on the job site as the ship to on the invoices would suggest. Furthermore, we don’t have any language in our sales contract specifically about the billing for stored materials process.