Filing officers with whom notices of federal tax liens, certificates and notices affecting such liens have been filed on or before January 1, 1968, shall, after that date, continue to maintain a file labeled “federal tax lien notices filed prior to January 2, 1968” containing notices and certificates filed in numerical order of receipt. If a notice of lien was filed on or before January 1, 1968, any certificate or notice affecting the lien shall be filed in the same office.