++++ Agriculture - Common organization of the markets - Milk and milk products - Additional levy on milk - Determination of reference quantities exempt from the levy - Account taken of exceptional events affecting production - Limits - Production affected in a year other than the reference year - Exclusion - Choice by a Member State of 1983 as the reference year - Variation of reference quantities - Account taken of the situation of a category of producers whose production was previously affected by an exceptional event - Whether permissible ( Council Regulation No 857/84, Arts 2(2 ) and 3(3 ); Commission Regulation No 1371/84, Arts 2(1 ) and 3 )