(1) The Commissioner shall, in the prescribed manner, institute proceedings for the purpose of determining the liability of a dealer to pay tax under this Act. Such liability shall be determined by an order and such determination shall be made within a period of twelve calendar months from the date of institution of such proceedings.

(2) Notwithstanding anything contained in sub-section (2) of Section 5, liability of a dealer to pay tax under this Act shall not be determined from a date earlier than five years prior to 

(i) the date of institution of proceedings under sub-section (1); or

(ii) the date of validity of the registration certificate,

whichever is earlier.