Thanks for reaching out about this. I know it can be concerning to have information missing when you've spent time entering it into your books. I want to make sure you're able to track down what's happened with these invoices to sort out your books.
In QuickBooks Self-Employed, invoices are handled through the Invoices section in the program. On that page, you'll have options to filter for the Status of the invoice as well as when it was posted. The program defaults to display the Last 12 months of invoices, so if the ones you're searching for are from beyond that period, simply adjust the filters in order to see more.
If after that you're still having trouble finding the invoices you're looking for, I recommend contacting QuickBooks Self-Employed support outside of the Community. With a one-on-one conversation, an agent can work with you to make sure you have the information you need in your books and let you know the steps to resolve this situation. Here's how to reach someone.