Perhaps you could explain why the BA code matters?

If it was under BA code then it mean "BA marketed", and so AY isn't usually minded to do this. If this is a Joint Business itinerary then it doesn't really matter, but still usually you would have to approach BA's contact centre to do this, and there are various other rules that apply depending on the specifics of your booking. More usually this sort of booking comes off a travel agency which has a close relationship with BA and thus looks to plate up a ticket in 125 as much as possible.