GP2013 PO Number on Check

The standard GP check format has the PO Number field available in both the work table PM10300 and the duplicate stub table PM10801 on the report. I assume this value is coming from the PO Number field in the PM Open Transaction table PM20000 when the voucher is selected for payment. There is a value in the PM20000 table but no value in the PM10300 or the PM10801 tables and nothing appears on the report when I add this field. Any ideas on why the PO Number field is not populating in the payment tables and/or how do I include this on the check stub payment line. Thanks, Dave