Such adjustment, for any fiscal year, shall be made by revising the national average per participant grant for nutrition services and administration for the preceding fiscal year to reflect the percentage change between—
(I)#
the value of the index for State and local government purchases, as published by the Bureau of Economic Analysis of the Department of Commerce, for the 12-month period ending June 30 of the second preceding fiscal year; and
(II)#
the best estimate that is available as of the start of the fiscal year of the value of such index for the 12-month period ending June 30 of the previous fiscal year.