Section 12(7) in The Central Sales Tax (Registration and Turnover) Rules, 1957
(7)The declaration in Form 'C' or Form 'F' or the certificate in Form E-I or Form E-II shall be furnished to the prescribed authority up to the time of assessment by the first assessing authority :Provided that if the prescribed authority is satisfied that the person concerned was prevented by sufficient cause from furnishing such declaration or certificate within the aforesaid time, that authority may allow such declaration or certificate to be furnished within such further time as that authority may permit.
