Originally Posted by
Flying for Fun
Indeed, BA awards have been a bit wonky. I was just looking at February 27th and was able replicate your scenario. BLQ-LHR only has IB availability showing so the multi-city would fail. LHR-ORD showed F but the through fare BLQ-LHR-ORD was J only on each segment.
BA doesn't offer intra-Europe awards. AY, EI, and IB offer intra-Europe awards. So it makes sense that the IB flights are the only ones to show up. It took me a second to realize this was the case. For BA options you have to find the day your TATL flight has the desired availability, then tack on the flight from the origin into LHR.