It is painfully apparent, in the later editions of the Institutes, that the discursive model was strained and its clarity of doctrinal exposition threatened by the addition of polemics that interrupt the flow of thought and frequently move in directions not dictated by the positive statements of doctrine. (p. 61)
The gradual expansion of Calvin’s Institutes manifests virtually no concern for approach, method, or over-arching unity until the final edition of 1559, when Calvin reorganized the whole of the Institutes on the pattern of the creed. Even in this final edition, the issue addressed by Calvin was the arrangement of all his chapters – including non-creedal topics – under the creedal form and not the development of a consistent approach, either synthetic or analytic, to the organization of doctrine. (p. 62)
From: Post-Reformation Reformed Dogmatics: The Rise and Development of Reformed Orthodoxy, ca. 1520 to ca. 1725: Volume One: Prolegomena to Theology by Richard A. Muller; 2nd edition (Grand Rapids: Baker Academic, 2003 ).