BA is quite good about taking coupons with wrong dates at the airport, even pulling multiple coupons (A-B-C for A-C non-stop) particularly if you are switching carriers ... all without a fee. They are sticklers for rules but sometimes that works to your advantage (when the rules are on your side, or there is a gray area and they want it). Best I can tell the extra GBP 25 fee levied by BA is only for ticket reissues when the USD 75 fee applies.