Validating data in an import scenario when adding a PO to an AP Bill

After importing the PO into the AP Bill I want to compare the unit cost provided in the import to the PO unit cost and mark the AP Bill in some way,  However, the Transactions.CuryUnitCost is not populated.

For example,the import file has $100 as the unit cost but the PO unit cost is $80.00.  The problem seems to be the Transaction columns are not populated and the condition is true every time,

The formula is =IIF([Transactions.CuryUnitCost]<>[Unit Cost],Concat('Unit Cost of ',[Unit Cost],' Not the same as PO Cost'),'')

Where [Unit Cost] is the source data being imported,