When paying an invoice I now have credits showing up from years ago that shouldn't be there

You can review the credit transactions for that specific customer to verify if any credits from previous transactions have been applied, @CindyO13. I'll provide some insights and guide you through the process below.

To begin, please note that credits from previous years may appear if they were misapplied, or duplicated, or there could be system issues that prevented them from transferring properly. As a result, credits can accumulate unnoticed. To confirm this, we can review your customer credits:

1. Navigate to the Customers menu and select Customer Center.
2. Choose the specific customer with the lingering credits.
3. Filter to All Transactions and select the relevant date range.
4. Review your transactions for any duplicate entries. 

If verified duplicate, you can delete the unused credits by following these steps:

1. Select the duplicate or unused credit for that customer.
2. Click on the Delete or X icon in the upper left corner.
3. Confirm by clicking OK to delete it. 

If it's not, I recommend generating a Transaction List by Customer report to identify discrepancies in your credit transactions. Here’s how:

1. Go to the Reports menu and select Transaction List by Customer under Customers and Receivables.
2. Select Customize Reports and filter for the appropriate date range.
3. Click OK and review the generated report. 

Moreover, you can explore this resource to gain a deeper understanding of how to issue credits or refunds to your customers: Give your customer a credit or refund.

I'll include this guide to assist you in adjusting your data selection, rearranging columns, and personalizing your report's style to suit your preferences: Customize reports in QBDT.

Please let me know if you have any follow-up questions about outdated credits or anything else related to QuickBooks. I'll be more than happy to answer them.