Document Ai Service

Hi I am using the document Ai feature for invoices, I need to get the purchase order number and the document ai service works great when there is a label for the field e.g. PO or Purchase order. We have certain invoices that will have the purchase order number added in a text section with no title, in this case the po number is not returned, I am working with the json data coming back from Document Ai Premium Service but it does not return any reference to the po number as it is not labelled.