For years in which DOH does not update the base year, subject to the approval of the Director of the Budget, DOH may use a compounded trend factor to bring base year costs forward to the appropriate rate period. The trend factor shall be taken from applicable years from consumer and producer price indices, including, but not limited to the Medical Care Services Index; U.S. city average, by expenditure category and commodity and service group for the period April to April of each year.