The report only shows carts that have been flagged as abandoned (the customer stopped adding items and let the automatic abandoned-cart timer expire) and are still open. As soon as the customer completes checkout the cart gets a close date and drops off the list – which is exactly what the abandoned-cart email is trying to achieve. The row is also tied to the cart's last-update date, so if the customer opened and edited the cart again later without checking out, look for it under that newer date.