What exactly do you want update them on? The fact that you have worked on your case study analysis skills? O you have developed your whole profile?
I think that it would be worth highlighting the things you have done ever since the AC, especially when it comes to graduating with a high grade, awards won, prizes or new societies you have joined, and internships opportunities.
I would not write how you have developed case study analysis skills and therefore you will perform better on the AC this. I believe that you should show this once you are invited for the AC again, which I am sure you will anyway! Show rather than tell I would say!