How to automate drop down list allocation given specific entries ?

Hey Alex

So from what you have written I have had another look at home. So I have put the drop down lists in the reference sheet. Then created a vlookup within the supplier invoices with if error ontop to remove N/A if there isn't anything in the field, it returns 0 instead of N/A.
The raw data will need to entered into the reference sheet, but any time you enter the supplier into the column a on supplier invoice it will pick up what you require. I copied this down 1000 cells. Let me know if this is what you mean