I check my image archives on my media server to see when the pictures were initially taken, and then bring up the spreadsheet from that month to see what it sold for. Of course, if it sold on a different month after the initial listing, I bring up a few at a time, the next spreadsheet and the few after that until I find where it sold.
You should have all of this type of data in your offline sales records. You do keep records, right?
If it works, sell it. If it works well, sell it for more. If it doesn't work, quadruple the price and sell it as an antique.
-- Ferengi Rule of Acquisition #80
