Hello, DavidDean.

I appreciate your time getting back to us. I have details regarding how the transactions are sorted with the current customization settings. 

You aren't misunderstanding anything at all. It's how QuickBooks organizes the transaction grouping. Sorting it by Vendor arranges the transaction by date and separated by vendor. 

One way to determine which bill isn't linked to a purchase order to check how it is placed using the current customization settings.

You'll want to look for POs that were grouped by linked bills (as what RaymondJayO has shown in his screenshot). Next, check placement of the bill and the amount to see if it corresponds with the purchase order amount. 

Finally, open either the bill or the PO to see if it's linked or not. 

Another way to do this easily (this works well if your POs are still open) is to look at the Open Purchase Order List report, then compare it with the bills in the Transaction List by Vendor report. 

Simply go back to the Reports page, then search for Open Purchase Order List in the box.

Next, export it to Excel to view the transactions easily. Click the "paper icon" next to the small gear, then select Export to Excel. 

Looking for help managing your vendors, expenses, or other financials? Feel free to visit our articles here. More topics are found at the bottom of the page. 

I'm always here to help, so leave your reply below if you have other concerns with QuickBooks Online.