So, I did find some more information about this.
Invoices stay on the main Submission Tracking page for 8 months. After that, you can locate the specific invoice information by entering the submission number in the search bar on the submission tracking page. Unfortunately, we are currently experiencing some issues with the submission tracking. Some invoices are not displaying properly, even when the information is entered in the search bar. We are working on that problem now and hope to have that fixed ASAP.
In the meantime, if you have any questions or need to check the status of an order, our customer service department can provide that to you any time.