The strategy in place for the product governs how each coverage period is summarized when shown to the a case worker (see Viewing a Determination's Coverage Periods, Viewing Key Decision Factors Graphically and Viewing Key Decision Factors in a List).
If you change this setting for your product, then it will affect how all determinations for the product are displayed, including historical determinations already created and stored as well as any new determinations created in the future.