Areas where rules were in effect on April 17, 2006 that differ from the rules set forth in subpart C are considered existing special use areas, and such differing rules remain in effect to the extent allowed by subpart A, and to the extent they are consistent with § 423.28. For those existing special use areas, compliance with §§ 423.60 through 423.62 is not required until the rules applicable in those special use areas are modified or terminated.