42 U.S.C. § 1320d–3

(a) Initial standards The Secretary shall carry out section 1320d–2 of this title not later than 18 months after August 21, 1996 , except that standards relating to claims attachments shall be adopted not later than 30 months after August 21, 1996 . (b) Additions and modifications to standards (1) In general Except as provided in paragraph (2), the Secretary shall review the standards adopted under section 1320d–2 of this title , and shall adopt modifications to the standards (including additions to the standards), as determined appropriate, but not more frequently than once every 12 months. Any addition or modification to a standard shall be completed in a manner which minimizes the disruption and cost of compliance. (2) Special rules (A) First 12-month period Except with respect to additions and modifications to code sets under subparagraph (B), the Secretary may not adopt any modification to a standard adopted under this part during the 12-month period beginning on the date the standard is initially adopted, unless the Secretary determines that the modification is necessary in order to permit compliance with the standard. (B) Additions and modifications to code sets (i) In general The Secretary shall ensure that procedures exist for the routine maintenance, testing, enhancement, and expansion of code sets. (ii) Additional rules If a code set is modified under this subsection, the modified code set shall include instructions on how data elements of health information that were encoded prior to the modification may be converted or translated so as to preserve the informational value of the data elements that existed before the modification. Any modification to a code set under this subsection shall be implemented in a manner that minimizes the disruption and cost of complying with such modification.