We did some change order work for our contractor by email request without a written change order (wasn't in the contract) and have yet to receive the change order to increase the contract for the work provided. Unfortunately, to my horror I realized I have issued lien waivers covering those months we did the work and didn't bill for so the amount was zero (oversight on my part). If we needed to, are we still able to file a lien for unpaid work we haven't billed for that covered those months we issued waivers?