Add Items From Open Purchase Orders
When on a Receiver, you need to add Items from other open Purchase Orders.
You can go to Admin > Company Preferences and click Receiving on the left and check the box for Add Open Purchase Order Items to Receivers
After the preference is enabled, when you open a Receiver, you will see the green Add Items from Open Purchase Orders button on the Items tab. Click the button to add the Items.
On the popup window, the No. column shows the Purchase Order number, find the correct Purchase Order and then click the check box on the left for each Item you need to add and then click Save.