I'll spare everyone a history lesson on little metal plates with the number 125 on it, and people using pen knives to lever out and swap over the plates, but yes BA can only issue tickets with a 125 number. These can be for any airline that BA has an internal agreement on the finance side. So you can get an FTV / EMD / eVoucher for 125 flights, what that voucher can be used for may be limited as quoted above, though it's only a few limited exceptions. If it is for a Vueling flight sold as BAnnnn then that's fine, it's BA marketed. In short, if you buy via BA.com or the contact centres then you are protected with BWC, in some cases you can't use it exactly to replace the services booked. If you look, however, there are all sorts of oddities that end up on a 125 ticket.