Yes, there's a way to run a report to get the information you need, @DavidDean. 

Let's pull up the Transaction List by Vendor report since it displays all the transactions per vendor. Then, customize it to see the purchase orders and their linked bills. I'll guide you how. 

1. Go to Reports from the left menu.
2. Enter Transaction List by Vendor in the Search box and select it. You can also locate it under the Expenses and Vendors section. 
3. Select Customize.
4. Set the Report period as to when the PO's and bills took place. 
5. Go to the Filter section. 
6. From the Transaction Type drop-dwn list, choose Bill and Purchase Order.
7. Click Run report.

The screenshot below shows you the last four steps. 

Here's a sample screenshot of the result: 

Once done, you can locate the missing bills that aren't linked to the PO's. 

Then, run either the Open Purchase Order List or Open Purchase Order Detail report to check those transactions that are still open. This way, you can apply them to the bills to mark them as Closed. 

In case you need to save the customization settings for the said reports above, memorize them. It helps you quickly access them in the Custom Reports tab for future use. 

Click the Reply button below if you have follow-up concerns regarding purchase orders or other inquiries. I'll gladly help. Take care.