Orders are placed by issuing a GSA 276 form, supplemental lease agreement. The start date is confirmed by a supplementary lease, executed by the lessor and the Government at the same time as the financial statements, and is not subject to any subsequent conditions, including, but not limited to, the completion or availability of all or part of the leased premises for use and use by the Government. The tenant undertakes to conclude with the lessor an additional rental contract with the lessor which fixes the start date of the lease. In such a case, the tenant and the lessor will immediately conclude a new additional rental agreement for the new real estate. The contract agent may recall the establishment of the property tax base by establishing a unilateral additional administrative lease agreement that indicates the base year, the amount of the property tax base and the percentage of government occupancy. . . .