The problem in producing both receipts is that there is no cross-referencing between the two tickets. Other airlines will give do something similar to the following.
They state
New Ticket Value= $1200 (BA doesn't show this)
Less Original Ticket Value exchanged(number included) = $1000 - (BA doesn't show this)
Penalty= $200 (BA doesn't show this)
Amount collected: $400.
I actually think I am entitled to a proper receipt for a transaction. I have nothing that shows me the fare of the new ticket. It's absolutely ludicrous. What if I need it for tax purposes???? They surely do, which means that they DO have the information but just are too incompetent to lay it out properly.