To me it does matter but I can understand the sentiment of writing a summary first. As dealt with in my book, Demystifying Business Cases ... I explain why the summary is better and much more easily written last. It is simply that A) upfront you do not know yet what the case summary at the executive one-page level is going to highlight and B) the smart way to write the executive summary is to lift the most powerful sentences and points out of the other seven sections to merge them into a flow that mimics our Nine steps; but your grammar and tense and all that fancy part is improved to make the whole story read better. This way, the copying and pasting method ensures you don't throw some new idea into the summary that is not adequately fleshed out in the case narrative.