Function to show if a new error record exists

At work, we have error reports as part of our data governance for SAP. The reports are run bi-weekly and put into an excel file, listing in rows the Material Number, Plant Number, Product Status, etc...

I want to write a function that will look at last weeks file and this weeks file to see when a new error has been documented for a material #. The problem is that the Material Number may have multiple errors on different rows because it has occurred at different plants.

I've tried something along the lines of (replaced cell numbers with column headers):

=IF(Vlookup(Material#,OldTable,OldTable.DisplayPlant,False) = Vlookup(Material#,NewTable,NewTable.DisplayPlant,False), "", "New Record")

This returns N/A and I've tried other types of similar equations and still no luck. Hopefully I have explained it in enough detail for someone to see what I am getting at.