We did something like @RobertWhite 's solution but I especially like his solution. I think @MadelineStefanou had set it up originally. Each customer was set up as a vendor in a special numbered series (REF0001 for the first refund that year, REF0002 for the second) and at the end of the year we'd merge all the year's refund vendors into a one new refund vendor number that included the year (REF2017, for example). That way if customer needed to find a refund, they'd only need to look thru that year's refund vendor number (REF2017).