Retrospective reopening power cannot apply to completed assessments where amendment enlarges the assessor's jurisdiction.

The unamended reopening provision under section 19(1) of the M.P. General Sales Tax Act, 1958 allowed reassessment only on the basis of information already in the assessing authority's possession. An amendment by Act No. 20 of 1961 enlarged that power and was substantive, because it affected the assessee's existing protection against reopening of a completed assessment. As no retrospective operation was expressed or necessarily implied, the amended provision could not apply to the completed assessment for 1959-60. Reopening on the ground that earlier accepted C forms were defective was therefore unlawful.

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Issues: Whether the assessing authority could lawfully reopen the assessee's assessment for the assessment year 1959-60 under section 19(1) of the M.P. General Sales Tax Act, 1958, on the ground that the C forms earlier accepted were defective.

Analysis: The unamended section 19(1), as applicable to the assessment year in question, permitted reopening only on the basis of information in the possession of the assessing authority. The amendment introduced by Act No. 20 of 1961 enlarged the reopening power and was not merely procedural, because it affected the assessee's existing right not to have the assessment reopened except in the limited cases permitted by the earlier provision. In the absence of retrospective operation, the amended provision could not govern the reassessment of a completed assessment for 1959-60.

Conclusion: The reopening of the assessment was not lawful, and the question was answered in the negative in favour of the assessee.

Ratio Decidendi: An amendment enlarging the statutory power to reopen an assessment is substantive, not merely procedural, and cannot be applied retrospectively to completed assessments unless the statute expressly or by necessary intendment so provides.

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