The prohibition in 223.7303 does not apply to—

(a) Legacy systems and their related parts, subsystems, and components that already contain hexavalent chromium. However, alternatives to hexavalent chromium shall be considered by the appropriate official during system modifications, follow-on procurements of legacy systems, or maintenance procedure updates; and

(b) Additional sustainment related contracts (e.g., parts, services) for a system in which use of hexavalent chromium was previously approved.