Originally Posted by
number_6
The stock is set in concrete for the life of the ticket. This is where the money went; changing the stock requires a fund transfer between airlines. Which of course happens as coupons are used, but on a reissue the ticket keeps its original stock. You would have to refund the ticket and issue a new one (not useful for OWE which have no refund value). Of course BA will be quite happy to sell you a new ticket.
I and many others on the board have reissued tickets with other carriers and after the reissue the ticket was on the stock of the carrier doing the reissue.