You can also go to "change" the ticket and select your flight the same day, it will then show you how much you paid and how much you can save or how much you would owe. At that point simply close the window without accepting the change. I do this all the time when re-fareing during sales. That way I can easily tell if the fare is less or more than I paid, much easier than sifting through a lot of confirmations or a spreadsheet. I do keep a spread sheet of all of my TTFs.