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If the big assignment really is that much more substantial and impressive than the other assignments then I think what you are suggesting is a great idea! Little assignments can add up to ultimately take a lot of time, however, and so if you think that there is a risk of the person reading your application wondering whether the big assignment alone is enough to explain your entire work experience, you may want to add a sentence or two at the end saying that you were frequently involved with additional proofreading and research tasks for a range of other assignments alongside this big assignment. I think it never hurts to mention everything you did, but do feel free to make the emphasis of this work experience entry about the big transaction