I actually never seem to have a problem. I get my fare receipt right after booking. Changes may look confusing....but just look closely. There is a line on the receipt that has the masked credit card number....that line has the value of the add collection (as well as a general fare value on the same receipt).
Finally when I do misplace a receipt...my Amex gives me the ticket number (starts 001). I print a receipt from the refunds website.