Firstly, how do they get transferred? I had a connecting flight on a single ticket and one was credited, the other wasn't. Another pair weren't credited at all, despite the BA number being on the ticket.
Secondly, why do they ask ME for certain details (like fare code basis) when surely they'd get better information (and hard evidence) from the airline themselves? If they spend 10 minutes writing me a letter, why not a 2 minute phone call to the airline concerned instead?
I've had this twice now - once with Emirates, the other with LAN [Chile and Peru]. Both were 4 flights each to be awarded to my BA account. The former took 7 months for BA to grudgingly award the 25% mileage.