I was on BA218 DEN-LHR last week and that was showing similar availability during the week beforehand. In fact it was showing pretty much 0 in Y & W for some weeks.
When it came to checking in I was offered an upgrade for $800 from WTP to CW which I politely declined after asking them to repeat the sum in question. No op-ups or UuA offered. On boarding everywhere looked completely full.
I guess BA prefer to get folk to pay cash if at all possible.