When looking at the Marketing UI in Commerce the total amount of orders are shown. This can be a bit misleading for users that want to see the amount of successful orders. A scenario where this is shown is when users have a credit card payment and made 3 different purchases with three different statuses. Waiting Exchange, Cancelled and In Progress. In the Marketing UI it shows that there have been 3 orders that has used this voucher code. But the most correct in this situation would to not show the ones that have been cancelled as they in fact is not a purchases order that has used this voucher.
By default the Marketing UI will not show the ones that have been deleted and at the very least it does not seem correct to count cancelled orders. This has been written up as a feature request so if you would like to see this in the product, please vote. http://world.episerver.com/support/Bug-list/bug/COM-5508